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Years ago, right after we bought our very first RV ‘Das Bus’, it sat in our driveway taunting me while I laid awake in bed. I was terrified at the prospect of having to jump feet-first into the sewage and waste management business of RVs. That terror intensified when I rolled up to my first dump station. I was so nervous about that first dump, I waited until late at night to head to the dump, thinking the chances of no one else being there would be better. But nope. As I pulled in, a couple big 5th wheels pulled up right behind me. Because that’s just how the universe works.

Even though having those other RVs there totally judging me (I was sure) added to my stress, I survived. But I still remember how it felt, and so I’ll always have a bit of a soft spot for new RVers learning the ropes. That’s my goal here, to pass on a few beginner tips on how to deal with your RV sewage—and hopefully save you a few sleepless nights.

RV Sewage System Basics for Beginners

The biggest difference between RV and home plumbing is that in your home, sewage pipes carry all your wastewater far, far away. But in an RV, it flows to waste tanks to collect, and then you get to deal with it later.

Your RV will have two or more of these tanks, which are usually plastic, and hang underneath your RV. Tanks called “black”, will contain toilet waste. Tanks called “grey” will contain water from your sinks and showers.

While the grey water plumbing looks and works very similar to household systems—with traps and sloping lines—the black water plumbing does not. When you flush an RV toilet, the waste generally goes straight down. There may be a bend in the piping, but usually the black tank is located directly beneath a toilet. There are no traps, or S-bends in the toilet drain to keep smells at bay. On many rigs, if you look down into the toilet, you can see the black tank contents directly below.

RV Waste Plumbing Best Practices

The best way to resolve a problem with your RV’s waste plumbing system is to never have the problem in the first place. These “Best Practices” should help keep your wastewater systems working the way they’re intended.

TIP 1: Water is your friend.

If you forget everything else in this article and remember just this, I’ll feel like I’ve done my job. I doubt you can cause a problem with your RV’s waste plumbing by adding too much water (well, except overfilling the tank). But you can cause lots of problems by not using enough water. Water in your RV’s waste system does a few important things. Most importantly, it dilutes the waste & dissolves solids so it drains efficiently. It also keeps the seals in your wastewater system from drying out and keeps things from getting stuck on your tank sensors. Plus, it helps manage odors, which can be quite a challenge in RVs.

TIP 2: ALWAYS keep water in your waste tanks.

This includes before trips, after trips, between trips, and I would even suggest during periods of non-use (like over the winter). I’ve made it a habit to immediately add some water every time I empty the tanks, so it’s just a part of my dumping procedure.

How much water to add is a bit fuzzy, but if you know your tank capacity, try to shoot for around 10%. That’s not a rule, and it doesn’t have to be exact. Adding a bit of water to your grey tank is as easy as running a faucet. To add water to your black tank, you can just fill the bowl with water and flush it a few times.

When storing or winterizing the rig, I still add liquid to the holding tanks. Depending on the
temperatures I expect, I’ll either add some RV antifreeze with the water, or skip the water altogether and just add straight RV antifreeze to the tank.

TIP 3: Use enough water when you flush.

It can be tempting, especially when boondocking, to be ultra-conservative with flush water. But doing so can lead to super concentrated sludge in your black tank. When that happens, it’s harder to get everything out of there, and it can set you up for future problems.

TIP 4: Leave some water in the toilet between uses.

Just an inch or so covering the bottom of your toilet will be enough. This is important for two main reasons. Remember—your toilet is gravity powered, with no traps or S-bends. There’s nothing between the inside of your rig and the contents of your black tank except the valve at the bottom of your toilet bowl. So, having a seal of water provides a vapor barrier to keep odors (gases) out. And secondly as I already mentioned, water keeps the seal on that valve from drying out.

TIP 5: NEVER leave the black tank valve open at full hookups RV campsites.

It might be tempting at a full hookup campsite to remain hooked-up to the dump with your black and grey valves left open for the duration of your stay. I don’t recommend this, particularly for the black tank. Have you heard of the “poo pyramid”? I’ve never experienced one, but leaving your black valve open is a common way this problem occurs in RV black tanks. When you do, the liquids drain away, but the solids (with no water to carry them) will just remain where they fall – usually right beneath the toilet. Over time, this mess can harden and, well, you get the idea. Nobody wants to deal with that, so it’s best to just keep the black tank valve closed. That way, the liquids can keep everything diluted and you’ll have no trouble getting everything emptied when you do eventually dump your black tank.

TIP 6: DO use a tank treatment.

I wrote a detailed post on holding tank chemicals and I very much recommend that as your next read, so I won’t repeat all that here. But in a nutshell, you want your holding tank treatment to do two things:

  1. Help (along with water) to break down solids.
  2. Eliminate odors.

After the section about “the poo pyramid”, it should be pretty obvious why you want to break down solids, and wanting to eliminate odors is a no brainer, but those are the two goals you’re always trying to achieve with tank treatments.

There are a lot of options for holding tank chemicals, and my holding tank chemicals article will guide you to choosing one that should work for your situation. It’s best to add your tank treatment while you’re adding the water to the tank just after emptying.

I’ll add here that you might consider adding a treatment to your grey tank as well. It’s not human waste, but the fats, oils, food particles, dead skin, hair, and soap scum that can accumulate in your grey tank can turn into something almost as nasty as your black tank. Personally, I don’t add a grey tank additive every time I dump, but I do it occasionally to keep the buildup down and the smells at bay.

TIP 7: Do use the right toilet paper, and use a little less than you use at home.

Notice, I said “the right” toilet paper. That isn’t necessarily RV-specific toilet paper. The main thing you want from your toilet paper is that it breaks down quickly and is septic-safe. There’s an easy way to test toilet paper, and I have a YouTube video of an experiment I did years ago with my 2-year-old assistant, “Baby”, complete with lab coats and Ball jars, so you know it’s a totally legit experiment… In our test, Charmin Ultra Soft actually won.

And while we’re talking about toilet paper, it goes without saying that you should not use any of the heavier-duty “personal wipes” in your RV’s toilet. I repeated the toilet paper experiment (with my same lab assistant Baby many years older) on the wipes and was never able to find one that broke down quickly enough to give me a real comfort level, so if you use them, don’t flush them.

TIP 8: Dump your tanks when they are 2/3 or more full.

Here’s the deal: when you empty your tanks, you don’t want the wastewater to dribble out. You want it to WHOOSH out! Faster flowing water will be better able to carry sludge out of your tanks, and the easiest way to improve the speed of the effluent is to just wait until the tanks are mostly full to empty them.

Sometimes, this might mean adding water to the tanks to get them to dump properly, like at the end of a trip. It’s OK to run your sinks and toilets awhile to get the tanks topped off before you dump. (Just please don’t do that at the dump station if there are people lined up behind you! Dump station etiquette is to get in and out as quickly as possible.) Like I said way back in the first tip, water is always, always your friend when it comes to black tank maintenance.

TIP 9: First the black then the grey.

Nobody ever told me this rule, but I figured it out intuitively my first time at the dump. Your grey water isn’t “clean”. But it’s probably cleaner than your black water. So by dumping the black water first, you can then “rinse” your sewer hose with the relatively “cleaner” grey water.

TIP 10: Don’t waste your ice.

One of the most popular videos I ever made was debunking the myth that adding ice to your black tank will “scrub” it out. I filled a clear black tank with simulated human waste (I got the recipe from NASA!) and a bag of ice and drove around like a madman with a GoPro in the tank filming it. Stef was motion sick and annoyed with me the rest of the day, but the results were worth it—if you haven’t seen it, it’s a fun (and educational) video, check it out!

At the end of the day, I concluded that the ice didn’t do anything more than plain water would have. In other words, you could have gotten the same results by filling the tank with water (your friend) instead of ice. If you think about it, it makes sense. Have you ever driven with an ice-filled Big Gulp drink? The ice isn’t knocking around all willy nilly in the cup as you drive along. It gently glides in unison side to side, without creating any real friction against the side of the cup. You can see that same thing in my simulated blank tank experiment.

To be clear though, the ice doesn’t *hurt* anything. So if you’re just going to dump the ice out when you get home, by all means, toss it down the toilet. But I wouldn’t buy extra ice just to put it in your black tank.

And that’s it!

There are a lot more tips and tricks we could get into, but these should get you going, keep your RV’s waste water systems trouble free, and hopefully relieve some anxiety. And if you’re headed to the dump station for the first time, and you’re convinced everyone else is watching and judging you… we’re not. (Well, as long as you don’t take too long…)