Inside the RV Black Tank: Testing the Sewer Solution

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I finished building my “Black Tank Simulator” a couple weeks ago, and ever since then, I’ve been itching to use it.  Stef quickly told me that playing with simulated sewage had to be an “outside” activity, so I’ve been waiting for good weather so I could conduct a proper test.  Yesterday, I finally got my chance.  Check out the video for details on the Simulator, what I used to simulate the waste, two complete tests, and a look inside the tank as I compare Valterra’s Sewer Solution to a standard 3 inch dump hose.


Observations from the tests

  1. If you’re out in your yard dealing with bright pink poop, the neighbors might stop to watch.
  2. The 3” hose emptied the tank in about a minute.  The Sewer Solution, as expected, was slower, at 2:30.  That’s a 2.5 : 1 ratio.  Again, this is entirely expected, but do keep it in mind.
  3. The 3” dump hose left more of the solids in the tank than I expected.  The materials left were items that had settled to the bottom.
  4. “Floating material” had a much harder time emptying through the Sewer Solution.  With the 3” hose, it was sucked right out.  This lends support to the traditional RV advice of waiting until the tanks are pretty full to dump.
  5. The slower emptying rate with the Sewer Solution actually had the effect of getting the sides of the tank cleaner than the 3” dump hose.  The 3” hose left a lot more of a slimy, greasy film on the sides of the tank.  This was something I had not expected.
  6. The tank flushing option on the Sewer Solution was considerably more powerful than I expected.  After using the Sewer Solution to flush the tank, it was unquestionably far cleaner than using a 3” hose.

My Bottom Line:

How useful the Sewer Solution is to you will depend on your style of camping.  If you move frequently, or boondock a lot without full hookups, then you’re a lot like us.  I tend to “dump & run”, mostly at public dump stations.  Given the extra time the Sewer Solution requires to dump; the need for a solid water hookup while dumping; and the fact that you’d probably want to flush the tanks as well to take care of remaining waste – it’s hard to see us using the Sewer Solution on the move.

However, if you are typically hooked up to a full-service campsite, and you have the time to use it – there’s no question that dumping and flushing your tanks with the Sewer Solution is going to get you a much better result than just dumping with the 3” hose.  If you’ve got the time and the facilities to do so, absolutely consider using the Sewer Solution.

Finally, we’ve got a class B, and storage is tight.  I don’t have the room to bring two dumping methods, so I’ll be taking the 3” hose on the road.  But I will definitely be using the Sewer Solution to flush out the tanks once I’ve returned home and have the time and facilities to do so.  I’d much rather have a well cleaned out tank waiting for me when we start our next RV adventure.

Well, that’s it for now.  If you have questions on the test or the results I saw, please leave comments below.  I’d like for these tests to improve over time, so I’m very interested in suggestions.  Also, if you have a product you’d like to see me put in action in the Black Tank Simulator, let me know that too.  And finally:

You can vote for what you’d like to see as the next experiment here!


Full Disclosure:  Valterra did provide the Sewer Solution I used for testing.  But they did not place any restrictions or conditions on my testing or reporting – beyond suggesting that I follow the instructions and watch their instructional video.  That seemed completely reasonable to me, and the opinions, procedures and results you see in the video are entirely my own.

James is a former rocket scientist, a USA Cycling coach, and lifelong fitness buff. When he's not driving the RV, or modifying the RV (or - that one time - doing both at once), you can find him racing bicycles, or building furniture, or making music. In his spare time, he works for a large IT company.

    67 thoughts on “Inside the RV Black Tank: Testing the Sewer Solution

    1. Mary Midgett

      Hilarious! Loved when you got sprayed with the flushing water, BUT, wondering if just sticking a hose with a spray wand down the toilet wouldn’t clean it out better. Also loved the scene of you in your kitchen making poop!

      1. James - Post author

        A number of people have suggested the “spray wand down the toilet” method. But testing that would be difficult. It would depend entirely on whether or not the operator pointed the nozzle at the residue. And since you (normally) can’t see it, that would be pretty random. I ultimately decided not to test that scenario.

        (Plus, Stef would never let me carry anything, dripping, through the RV that had been inside the black tank…)

      2. John Talley

        I am on my 5th self-contained RV over the past 30 years. When I stay some place with full hookups I drain my black tank and stick the handle of my toilet brush in the toilet holding the valve open and water flowing down the drain. I leave it running for 2 or 3 minutes after the tank water, as seen through a clear acrylic elbow, is clear.

        Never a tank problem on any unit.

      3. Lee

        Your videos are informative, well thought out and humorous. A good combination. But most everyone uses an additive of some sort in the black tank, how much difference do you think that would have made to the T.P. and pink poop tests?

        1. James - Post author

          I don’t think it would have made much of a difference in these tests. Even if you use an additive, there will always be chunks, sludge, etc, in the tank.
          Get a clear attachment for your sewer hose some day and watch what goes by…
          Not exactly entertaining watching, but informative I suppose.

    2. Roger Struthers

      Great, concise and fluid presentation. I did not go thru all of the comments and I may be repeating one posted. My RV has a built-in rinse spray for the black water tank that does a better job of cleaning the tank when it gets close to being totally empty. This process is the best of both processes in that it allows the tank to empty thru the 3 inch hose at full volume then rinse with fresh water from INSIDE the tank. Wish you had mentioned that system, but maybe yours did not have it. One other thing for those who don’t have an in-tank flush is they can use a 5 gal bucket of water down the toilet at the end of the dump. Again, great video.

    3. earl balentine

      I only dump when my black or gray tanks are full and always dump the last day at the RV Park. I used TanktechRX in my black and gray tanks. When I dump the stuff in the black tank is all liquified for the TankTechRX solution.
      I use a standard 3″ hose to dump. I always turn on my santiflush connection while dumping the black tank. I will let the water run for 15 minutes, stopping to back flush my gray into the black. When I am done I’m pretty sure the tanks are very clean. I have a scope camera an d have looked into the tank after dumping so I feel pretty sure it clean in there. We never dry camp so I might get a sewer solution macerator down the road. I could use the extra space.

    4. rottenrollin

      I’m a rocket scientist, too. When I was a kid I used Estes rockets and my own improvisations (including flame throwers) to terrorize the neighborhood…….

      But now that I’m an old coot, I can’t figure out my current “permanent” rv poop problems…….Tanks full to some unknown level…….it drains when more is put in……it’s backed up INTO the toilet……previous such would be relieved when using a plastic tubing into the toilet to break some unknown barrier……I don’t BELIEVE it is a valve problem, as i get some flow when valve is opened, which cuts off when valve is closed. I keep Black CLOSED except for dumping times. When they work. Often I will let grey water fill up and use it to back flush black tank, and this has helped a lot…….UNTIL NOW.


      My wife is ready to rent a miniature submarine for ME to shrink into and go explore the shtty problem. No Thank You !!!

      I’ve used a plastic tubing to relive this in the past, pushing it down the toilet until breaking some unkown barrier when WHOOSH, it all goes down……..
      Hallelujah, forgive me, Father.

      But for the first time that extreme is not working…….and the toilet remains full of the stinky brown stuff, and wifey does NOT appreciate the 5 gallon bucket with a potty lid on top of it that I have brought in.

      So what to do? What to do? I feel like some pressure is building withing the RV, soon to explode like Robin William’s experience in the movie RV.

      An Old Faithful of RV poop?

      Donna wanna go there.

      Is our black tank one huge mound with a tiny trickle through it…..until now?

      Has Robin Williams come back from the netherworld to haunt OUR RV ???

      Are we going to have to call the local porty potty people to bring us an outhouse?

      Tune in tomorrow for the exciting conclusion………..


    5. Jerry

      I don’t understand why you compared a double dump with the sewer solution to only a single dump with the 3-inch…how is that a fair test?

      1. James - Post author

        Perhaps not completely fair, but the standard 3 inch hose doesn’t provide an easy means to get a “rinse cycle” without buying something else, whereas the sewer solution does.

    6. wes

      When I was a wee lad my job when we were traveling in our rv was connections. We had water system that was a direct connection with city water. There was no gravity fill. On that direct connection was a pressure gauge so when you were surprised about the psi of you water at the house I was not. . It is high for sure but I have seen close to that before. Yoho was probably the highest reading I had ever seen it was well beyond the meter but I just did not open up the valve all the way to fill the tank. Wish I had a picture of that as the pipe attached to the fawcett was so long I could not see where it ended as it disappeared some where up the mountain. We had a hand pump inside the rv to pressurize the tank which worked rather well.

      1. James - Post author

        I have no idea how long the pressure had been that high. There was a pressure regulator on our home, but it had (obviously) failed.
        It’s since been replaced!

    7. Greg Lankford

      Thank you for the detailed test. I ordered a sewer solution today for a permanent setup but then I began to think about the fact that I am in draught-stricken California and I am concerned about the amount of water that it uses to empty the tank. It would be great to know if it is a 1:1 ratio, higher, or lower. I have a 50 gallon black water tank and using 50 gallons of water to empty does not seem very wise for our well. It is really difficult for me to run a 3″ ABS to the septic tank so I am in a pickle. A macerator pump might work but seems pretty costly. I have to pump about 100′. Any suggestions or insight into this would be greatly appreciated and helpful. Thanks so much!

      1. James - Post author

        Well now – that’s an interesting dilemma! I can see why the Sewer Solution might work out well for you, and I can also see why you wouldn’t want to use one. I’ve never been a fan of macerator pumps (just something else to break down – and then who wants to repair a clogged sewer pump??!!). In your situation, the sewer solution does seem like the best alternative, except for the additional water.

        As you’ve already ordered it, you might try to figure out the water usage on your own (without the sewage). If you could get a flow rate in gallons per minute, you could then just time how long it took to empty your tank and that would give you some idea of the amount of water used. Good Luck!

        1. James - Post author

          That made no difference at all. (It’s not like it creates a vacuum in there or anything.) See the next video in the series where a tank lid and vent was added.

      1. James - Post author

        Stef would never let me drag a wand like that through our RV! So I never tested it.
        But if you can imagine squirting a hose, you kind of have an idea what it would look like. The effectiveness of such wands depends on your ability to hit your target. And since you can’t really see down there, it’s anybody’s guess!

    8. Jennifer k

      James, I hv a Ss agile, do u hv a video to show how to hook up a sewer solution with an Ss agile. Don’t know how to do that. Thanks jennifer

      1. James - Post author

        Well, I don’t have any experience with the SS Agile. But in my experience, these sewer connection fittings are pretty standard. The Sewer Solution should twist on and lock the same as it does on any other RV. Good Luck!

    9. Don Petersen


      Thanks for the insight into the black tank.

      I have been using Sewer Solution for 15 years (5 as a full timer). I always use the 3″ hose at public dump stations. Mostly I dump in full service RV parks. One of the benefits of the Serwer Solution that you overlooked is that I can leave the grey valves open all the time (I don’t need the grey water to flush the dump hose). Thus I never have the problem of forgetting and having the grey water flood the bathtub (and the stuff we store there). Another benefit is that I can open the black valve and walk away confident that nothing bad will happen. I would never walk away while dumping through a 3″ hose.

      Have a great day,

    10. Langly

      Watched your video and would really like to see you do the same Test but with the “FlushKing”, and much more toilet paper – seems we go through a lot of that. Thanks

    11. Dennis D

      Just watched the video. I have been using the Sewer Solution for some time and we are full timers who use full hookups. I’ve often wondered how well the system was working and you definitely reduced my concerns. What I didn’t realize was how much the water would go back into the tank in flush mode. I realize you had lots of pressure but even at lower pressures I would expect some good flushing action. Thanks for the test. Keep up the good work.

      1. James - Post author

        Hey Dennis. You may want to have a look at the second video in the series – and then have a look at your plumbing configuration. The effectiveness of the Sewer Solution is greatly affected by the addition of bends in the pipe. If you’ve got a straight shot back like the test tank in this video though – you’re good! Thanks for watching.

    12. Robert

      I always wonder what the inside of the black tank looks like & what is the best way to rinse it. I have an older 1987 travel trailer so there is no hose attachment to aid in rinsing the tank. There is no monitoring panel for the tank levels either. The only way I can see how full the tank is & the condition of what is in there is to periodically look thru the toilet into the tank with a bright flashlight.

      I’ve come up with my own method for rinsing the tank- prop the water valve open until the water level is at floor level(i.e. tank completely full) & let it sit overnight. My theory is whatever is on the sides & top of tank will be dissolved in the water. Then I dump the tank the next morning & hopefully the huge rush of water will carry everything out of the tank. Then I repeat this process one more time. I also do this process when I winterize the trailer.

      1. James - Post author

        Well, it sounds like you’ve hit on one of the key points for black tank maintenance: Lots of Water!
        I see nothing wrong with your approach, but you might get even more benefit out of the soak if you add some kind of holding tank additive while filling the tank. (But I haven’t tested them yet, so I can’t say which one is best.)
        Thanks for reading!

        1. Robert

          James, good suggestion about adding an additive while soaking the tank. They’re so many of them out there though. I usually soak & dump just once during the season as it seems to be a big tank. Then I do a final soak & dump when winterizing. Don’t know the capacity of it but I timed how long it took to fill by propping the water valve open and it took 30 minutes. Assuming the flow rate is 1 gallon per minute that could translate to a 30 gallon tank?

          This summer I tried a formaldehyde based tank deodorant from Thetford. It comes in small bottles(6 per box) that you empty into tank. It didn’t work that well. With each bottle the tank odors were minimized for only about 3 weeks on average.

        2. James - Post author

          I’m impressed that you can go for 3 weeks before needing to dump! Stef and I are doing well if we can make it to 3 days!
          Personally, I’ve used the Thetford additive you mention. It will be included in my additive tests. But I’ve never asked it to sit for three weeks.
          You must have an enormous tank. Other than adding 5 gallon pails of water, I don’t have a good way to estimate or calculate it for you. But it sounds big.
          I’ll have a better idea what kind of additive to recommend for you after I’ve tested a bunch of them.

    13. Heather

      Thank you for taking the time to make your videos! It has helped me to understand how the SS works and I think that I would like to gain back the space that all the stinky slinky takes in our storage area!

      BUT we have two grey tanks and two black tanks on our Fifth Wheel so I would need for the system to connect via a “Y” someplace. I would purchase two SS, but the hose would need to connect downstream someplace to allow double dumping at a single sewer station. In your opinion, how easy would be it to modify it to allow for this sort of set up?! Do you think that the pressure/flow of the system would push the liquids up into the other tank?!

      Very curious if this could work for us!!

      1. James - Post author

        Heather, I had a look at our sewer solution, and read the instructions, and you’re in luck. The downstream end of the SS is regular 1″ schedule 40 PVC pipe. You can buy all the fittings you would need at any local hardware store. It should be no problem to create a “Y” connection into the sewer inlet. If I can get this picture to show up, here is a close up of what you’ll be working with. It’s all press-fit.
        The sewer end of the Sewer Solution
        When hooked up a a campsite, you would hook up your “Y”, and leave both grey valves open. DO NOT keep a pressurized hose (the water power source) hooked up to the Sewer Solution, except when dumping. With just the grey valves open, and no external pressure, gravity alone should keep things flowing the right direction for the grey water.
        For dumping the black tanks – you would do these one at a time. Hook the pressurized hose only up to the one you are dumping. At that time, keep all other valves closed.
        Hope that helps. Good Luck!

    14. Bob Lantinga

      I use the 3 inch dump hose. I put ice in the tank and put a gallo now water in the tank as well as the chems need to keep smells down. So the first ten minutes of driving after dumping the ice floating on the water I think clean the tank good. So don’t think anything in the tank sticks. What you think about that idea?

      1. James - Post author

        Hi Bob – Many people claim that the ice-cubes-in-the-tank thing really works to scrub the tank. It’s something I’ve not tried… BUT!!! I’m working on a video where I try the ice cube thing in the clear tank. I think it will give everyone a better idea of whether or not this actually works. Stay tuned. I hope to have it up in a week or so. Thanks for reading!

    15. Larry Holman

      I found the video very interesting and and informative. I think to have properly tested the 3″ tank drain with normal 3″ nose connected, one should have at least included a wand you insert through the toilet. As demonstrated in your video, you did back flush with the 1″ system but there was no tanks flushing done with the 3″.

      Keep up the good work and happy camping to you and yours.

    16. Lewis Deen

      First of all I want to thank you for your blog and site. Very well done. I have been using Sewer Solution by Sewer Solution rather than SewerSolution by Valterra, and I do not know if there is a difference. I have used the unit I have for several years and I really prefer it over the 3″ hose just because it is less messy for me to handle. I also like the fact that I can use plain PVC pipe to extend the reach. Another advantage is that when two of us are camping together, we can get two hoses into one 3″ sewer connection. Thanks again for the good work.

      1. James - Post author

        Welcome Lewis!
        Agreed, there are several other benefits the sewer solution offers over a 3 inch hose. One of my future experiment suggestions is for more experimentation with the Sewer Solution, I may test these kinds of things when I get around to that. We just got back from a 3 week RV trip, and I’m a bit behind on things, but I do hope to get started on the next experiments soon.
        And I don’t know if there is any difference in the Valterra vs. Sewer Solution branding. Interesting…
        Thanks for reading!

    17. Dean

      Great demonstration. Someone will always find an alternative to your test process and suggest you do it.

      So here goes. 🙂

      Because the SS uses water to assist the tank emptying via the small hose, I have tried to minimize the amount of water used to rinse and dump.

      My theory, which has no demonstrable foundation, is to interrupt the SS outflow of waste with a 15 second rinse mode to keep moving water in the tank and move stubborn stuff around to exit position. Hopefully that practice speeds the outflow of waste and provides a more efficient volume removal.

      5 minutes of rinse water in your experiment would be at least triple the rinse time I have ever used. As mentioned, the water pressure is probably not representative either.

      Basically, I like the sewer solution for ease of storage and transport, cleanliness of handling, and the uphill movement of waste when needed. How fast it dumps is usually irrelevant except at a shared dump station.

      My concern is seldom how clean my black tank is. It is going to be used again for the same purpose. Kind of similar to mowing the grass, except the grass is in front of the house for everyone to see.

      No one sees inside my black tank…….!

      Thanks for your creative and interesting experiment video.

      1. James - Post author

        Hey Dean – Glad you liked the video!
        And you’re absolutely right – I’m certainly not running short of suggestions for my next experiment!
        You’re not the first one to suggest a “short bursts” approach with the Sewer Solution. I will keep that in mind when I get to experimenting with that one more. (It’s one of my suggested experiments in the next post.) And I do agree, the Sewer Solution offers a few advantages that other rinse or dump solutions don’t. If you haven’t voted for the next experiment yet, be sure to vote in the next post. Thanks again!

    18. Jerry

      The high water pressure makes your testing wrong. I have been RVing since 1969, and never found water pressure that high.Most camogrounds are under 40 lbs.

      1. James - Post author

        Wow Jerry – That’s a lot of RVing!
        The water pressure is high. And in my follow up post, I decide to include a pressure regulator in future tests, which should remedy that. But don’t forget, where the pressure really made a difference was in the rinsing. The other parts of the test are still representative. You should go ahead and vote for the next experiment! I’m guessing your vote is for the tank rinser comparison.

    19. Danny Taylor

      I really liked the video. My coach has a factory installed flush that you connect to a water hose while dumping. I have always questioned how well it actually worked as it never seems to add enough water under pressure to clean the tank.

      Is there some way you could test these to see how well they actually do work?

    20. jackfish

      James, I look forward to your experiments with tank treatments. Please note the costs of each. I would also hope you would use Happy Camper in the treatment comparisons. For a 20 gallon tank, two tablespoons, costing as little as 27 cents, would be the right amount. It would alleviate the condition you found in 4. above as it dissolves toilet paper and liquifies waste. Thanks for your efforts!

      1. James - Post author

        Happy Camper is one I hadn’t considered. I suppose there are literally hundreds of treatments I could test, but I’ll keep that one in mind. I didn’t mention this, but for the additive experiment, I would want my simulated waste to be as close as possible to the real thing – chemically speaking – to be sure the results were actually representative. Someone posted a link to a NASA recipe for just such a thing, that I may need to check out as well. Thanks for the suggestions!

    21. Punomatic

      When I bought my first RV, the guy who did the PDI told me, “Always dump the black tank, then fill the toilet bowl to the top and dump it. Repeat that three or four times, and your tank will always be clean.” I have followed that advice and never had any problems with odor or clogging*. I would be interested to see a similar experiment in your test tank. To wit: empty the tank with the 3″ hose; then with the valve open quickly pour about a gallon of water in the tank 3 or 4 times.

      *(Except the time DW decided that “flushable wipes” were flushable in an RV! Ironically, I was using a Sewer Solution to dump on that occasion. The wipes plugged the outlet hose, and I had to dismantle everything and clean it out to complete my dumping routine. Yuck!!).

    22. Tom Boles

      Hi James,

      One more thought is the height of the outlet above your sewer clean out. With the 3″, it has the effect of increasing the velocity of the good stuff on the way down the hose, causing the tank to drain quicker. I don’t the same effect with the Sewer Solution would be seen. The jet pump effect provides all the positive pressure you need.

      I agree with the folks commenting on the line pressure. Thirty (30) to fifty (50) PSI is more than enough for the SS to operate and flush as designed. I guess I can understand the squeamishness about using your regulator, but remember, that is why the backflow preventer is inline to begin with!

      On the “real world” nature (or lack of it) of your rig, since you are doing comparative tests, you just decide how close to “reality” you want your test set up to be and test away. As with any test attempting to duplicate real world conditions, YMMV.

      Test Ho!


      1. James - Post author

        Lol! Well, a composting toilet won’t really work for us. But even if it did, I don’t know that I’d go that far in the quest for additional fresh water capacity!

        1. James - Post author

          Hey James – it’s future James!!
          Guess what – you just used a composting toilet this morning! You get one in your new Travato.
          Once you do some more digging about them, you’ll figure out it can work for you.
          (But still… don’t try to put fresh water in a former black tank… ewwwww!)
          Have fun!

    23. Gary

      Interesting video. I’d like to see the 3″ outlet pipe with an angle in it, as most tanks do not drain straight out. Many have at least 1 90 degree angle. My black and grey each turn 90 degrees towards each other, and then join in a Y just after their respective valves, so that each runs through a 90, then the valve, then the Y (effectively another 90) to the outlet. Also, as mentioned above, a wider/longer but shorter tank would be more realistic as well. A tall tank means more pressure at the outlet, which increases the velocity unrealistically.

    24. John Garay

      Very interesting. However, I have several comments: 1 – How often do you find 120 psi in CG’s? At that pressure, a lot of hoses would probably rupture. 2 – It would be interesting if f you reran the test and used your Watts Pressure Reducing valve to verify the results would be similar.3 – The sewer solution had the advantage of a secondary rinse at 120 psi.

      With your setup I think it would be interesting to see how other methods might effect the cleanliness of the tank when used with the 3″ sewer hose and normal psi. If I could suggest: Comparing the Camco Dual Flush to the Valterra Flush King; compare the Camco Flexible Swivel Stik Tank Rinser with the installed Camco Quickie Flush or the Tornado.

      I think a secondary rinse will give you a cleaner tank. I’m looking at the Quickie Flush and the Tornado as a better solution than having to go back inside your unit and using a flexible swivel stik.

      Thanks and looking forward to future testings.

      1. James - Post author

        I agree that 120psi is more than most could expect. I thought about using the pressure reducer in line. But it’s the only one I have and since we drink through it sometimes, I just couldn’t make myself do it. Even though it’s only simulated waste, I still couldn’t. What I *could* maybe do is get one of the less expensive regulators from Camping World or somewhere, and use that instead. They’re only a few bucks. I’ll do that in future runs where I use water to rinse or flush. The Tornado is an interesting idea for a tank modification. It’s also not too expensive.

        Thanks for the suggestions!

    25. Lorna

      I look forward to seeing the results of the various tank additives. Particularly the TP digesters. As a fulltimer who sits in one spot long term, the TP is a problem at times. We have recently started using a TP digester for the first time in many years. I suspect it has to do with the design of the RV waste tank we are using. Our last tank was desinged differently and we never had a problem. Time for us to make a new tank.

    26. Bill Pounds

      Nice job on the tests and the video. One thing that came to mind for me is that your tank dimensions do not simulate the most common black tanks in use in RV’s. Actual tanks tend to be long and wide, but not very deep, while your tank is very deep. I think that difference is significant with regard to how much sludge is left on the bottom. The actual black tanks have more bottom area, and my guess is that this would change your test result. Food for thought anyway. Thanks.

    27. Will

      To be fair, you should have hooked up a Flush King or Hydroflush with the 3″ hose, and did a flush afterward with that as well. I think you’d find that the tank ends up just as clean as it did after flushing with the sewer solution.

      When/if you do a more apples to apples comparison that way, I think you’ll find that the traditional 3″ hose solution (with flushing afterward) gets the tank just as clean as the Sewer solution does (with the possible exception of the sides of the tank), but does so much, much quicker.

      1. James - Post author

        Thanks, Will. You’re not the only one to recommend an aftermarket flush system. It seems like an easy enough modification to the simulator. I’ll add it to my list for future experiments. I’m just getting started!

    28. Mom

      What would happen to the dump rate and cleanliness of the holding tank using the 3″ hose if you pressurize the tank to 20 psi?

      1. James - Post author

        Mom? Uh, well, a properly working RV black tank has a vent stack, so the pressure should never get higher than the atmospheric pressure. If the tank somehow did pressurize, it would blow back at you when you flushed the toilet, and that would give you a pretty strong indication that something was wrong. But if, somehow, you could pressurize the black tank, the results of the test you describe would be… explosive.

    29. Roy Christensen

      As a former science teacher, I appreciate your careful testing methods! May I suggest that you try using the GEO method (adding dish detergent + Calgon water softener to the black tank) . I use a 3″ hose to empty the tanks in my motorhome. The black tank has a tank- rinser built in that i use when FHUs are available. The clear extension attached to the drain before the hose tells me that the tank-rinser works better than when I do not use it. maybe you can test these two variables. The tank-rinser is mounted about 3/4 above the tank bottom.

      1. James - Post author

        I’ve thought about adding a tank rinser to the test rig. I think I may – once I’ve run out of experiments with just the plain tank.
        A reader on another forum suggested tank additives as well. Maybe I could compare several. The trouble with that one is time – I’d have to let the tank sit around while the enzymes/blue stuff/etc. did its work. And then the similarity between my fake waste and the real stuff becomes more important. Your recipe though is pretty mild, and may help keep debris off the walls regardless of emptying method. Good suggestions! Thanks!


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