RV Black Water Tank: 6 Things You Need to Know

Last updated on January 18th, 2022 at 10:21 am. Originally published on November 14th, 2019

Your RV’s black water tank is a very important piece of equipment: it’s the tank under your rig that holds the waste water from your toilet. And while where everything goes when you “go” is no one’s favorite thing to think about, it’s part of what makes RVing so much more convenient and enjoyable than regular car travel or tent camping — no more relying on rancid pit toilets at the campground!

Of course, if you want to keep your RV’s black water tank working properly and whisking away your waste, there are a few things you absolutely need to know about how it works.


Here are six things to know about your RV septic tank… before you go.

1. What is a RV black water tank?

RV Black Water Tank
New RV Black Water Tank – Photo Credit: ebay.com

Most self-contained RVs have two types of waste tanks on board: a gray water tank and a black water tank. A gray water tank collects the water that goes down the drain of your RV shower and sinks. It is the presence of soap residue and dirt that give this waste water its name and gray-ish look. For more on grey tanks, check out this article.

What we’re concerned with is the other one: the black water tank, which catches the wastewater from your RV toilet. It’s called a black water tank… well, let’s just say, it’s called that for obvious reasons. This is what allows you to use your RV’s onboard facilities without having to worry about being constantly hooked up to a sewer connection (though a city sewer is the only place you should ever dump your RV’s portable black water waste tank!)

The black water tank collects both liquids and solids, so caring for it is a bit different than your gray tank. In addition to human waste, the RV black tank also collects water used to flush the toilet, and of course, toilet paper. Which, by the way, should be RV-specific toilet paper, which is more easily degradable and less likely to clog your rig’s sensitive plumbing system!

2. How do I clean my RV black water tank?

Cleaning Black Water RV Tank
Image via Amazon

Knowing what your black water tank holds, the next logical question to ask is: how the heck do you keep it clean and odor-free? What kind of RV black water tank cleaning chemicals are the best? Should you add bleach?

Fortunately, the availability of commercial chemicals and deodorizers makes it pretty simple to maintain your black tank on a regular basis. At the start of your camping trip, you should add a dose of RV black water tank treatment, which may come in liquid form (like Aqua-Kem) or in Tide-Pod-like packets (such as these, made by Firebelly Outfitters). Be sure to add in about a gallon of water, as well, which helps the chemicals do their job. Along with keeping tank odors down, these chemicals also have the ability to break down solid waste and toilet paper. That makes for a much smoother process when it comes time to dump your tanks — which we’ll get to in just a minute.

Along with maintaining your black water tank with these cleaning solutions, it’s also important to deep clean your tanks on a regular basis, perhaps between camping trips or before putting the rig into storage. You can run a solution of soapy water through your RV’s tanks in order to facilitate RV black water tank sensor cleaning, which will help ensure your sensors give you an accurate reading on the contents of your tank next time you go camping.

And if you do get a clog in your RV black water tank — which can happen, even if you use the right chemicals and toilet paper — there are a variety of methods for getting things back on track. You might try ice cubes or boiling water, for instance; click here for the full details on how to deal with a clogged RV potty!

3. How often should you dump and empty your black water tank?

How often should you dump and empty your black water tank

When you’ve gotta go, you’ve gotta go — and the same can be said for your RV! Of course, the exact frequency with which you need to dump and empty your tanks will vary, just as it does with how often you need to go.

For instance, if you’re traveling alone and frequently spending days outside of the RV adventuring, you might be able to last a week or longer without dumping the tanks. On the other hand, if you’re camping with a big family (or traveling in a smaller trailer or motorhome whose tanks aren’t exactly gigantic), you may find yourself emptying the tank every other day or so.

Most self-contained RVs have a sensor that tells you how full each of the tanks are, including the black water tank as well as the gray water and potable water holding tanks. However, with some smaller trailers, like Casitas, there’s no sensor. Rather, you just sort of… figure out that it’s time as the water level rises.

At the very least, you should dump and empty your black water tank after each camping trip, as you don’t want to store your RV with wastewater in the tanks! In fact, you’ll want to thoroughly flush your system — which we’ll talk about in the next section. But first, let’s go into how to dump the black tank on your RV, step by step. Looking for a dumpstation nearby? See this page!

4. How do I dump my waste from my black water tank?

To dump your RV’s black water holding tank:

  1. Connect a high-quality, reliable sewer hose to the outlet drain of your RV’s sewer system. You’ll see that there are two valves, one for the gray and one for the black water. Always drain the black water first. That way, you can drain the gray water afterward, which will clean the hose and dislodge anything that got, um, stuck. Ensure the other end of your hose is tightly fitted into a city sewer inlet.
  2. Pull the black water valve and let the tank drain completely. Once you can hear that it’s completely empty (no more sounds of water rushing through), close the valve and pull the gray water valve. Let that drain completely as well, and then close it. It’s good practice to keep both of your tanks closed at all times, even when you’re set up at camp and connected to a sewer. If you let the black water tank drain freely, liquids flow through but solids get stuck, leading to a very messy situation. And by keeping the gray water tank closed off, you’re always building up soapy water that can be used to flush the detritus of your black water draining process through the hose!
  3. When disconnecting the hose from your RV, move slowly — and consider rinsing the sewer hose with fresh water before you disconnect the other end from the city sewer connection. Store your hose, ensure your tank drain is tightly closed, and voila: you’re done!

5. What is RV black tank flushing?

RV Black Water Flushing

Some RVs have a built-in RV black tank flush system, which allows you to connect a hose directly to an inlet valve to essentially power wash your tank. This makes it super simple to ensure your tanks are sparkling clean. However, you’ll want to follow your manufacturer’s instructions to ensure you’re using it correctly. Most guides suggest you leave the black tank valve open, so that water doesn’t back up and end up flooding your RV through the toilet!

If your RV doesn’t come with a built-in black tank flush system, it is possible to install one aftermarket. This type of after-market option comes in many shapes and sizes, and typically requires drilling a hole in your RV black water tank.

Lastly, if you don’t have a manufacturer’s tank flush valve, and you don’t wish to add one to your tank yourself, you will need to employ a more manual method of RV black water tank cleaning.

One of the more popular options, for an RV black tank cleaner, is to utilize a garden hose extension called an RV holding tank rinser. Camco makes a great model called the “Swivel Stik” that many RV owners swear by. This rinser is designed to spray water in multiple directions, in order to clean debris and tissue from the sides of your RV black water tank.

Other owners also utilize the ice cube method mentioned in this post on cleaning your RV’s black water holding tank sensors. Add in some mild detergent, like Dawn or Joy, and you’ve got a great homemade black water flushing process!

6. Portable RV Waste Tanks

Portable RV Waste Tank
Image via Amazon

If you camp in the same spot for long periods of time without sewer hookups, you may find it necessary to take advantage of a portable RV waste tank.

These waste tanks allow you to empty the contents of your black and grey water tanks into an external tank, which you can then transport to a dump station. RV portable waste tanks usually have wheels and a handle, so they can easily be pulled across the campground for dumping.

It is important to realize that if you use a portable RV waste tank, you should take the same care to clean and flush it, as you do with the onboard RV black water tank.

Dealing with your RV black water tank is definitely one of the more unpleasant areas of using an RV, but the comfort and privacy that having an RV toilet on board affords you and your family is one of the biggest advantages to having an RV. Understanding your RV black water tank, and how to clean it, will give you years of comfort and odorless enjoyment.

Frequently Asked Questions about RV Black Water Tanks!

To close out this post, a few frequently asked questions — and their answers!

What’s the difference between gray water and black water?

As mentioned above, gray water is the wastewater that comes from your sink taps and shower — whereas black water is the waste that comes from your toilet. See our guide on RV water tanks and RV holding tanks for more.

How accurate are the tank monitors?

The accuracy of your tank monitors depends on how often you clean them! Here’s how to clean your RV’s black water tank sensors.

Best practices for dumping?

As mentioned above, always ensure you’re dumping your holding tanks into a city sewer connection made specifically for that purpose — never out onto the ground or into a street sewer a la Christmas Vacation! It’s also a good idea to keep your valves shut and wait until the tanks are full, or nearly full, to dump, as then you have the help of gravity (and a lot of gray water to wash the icky stuff through the hose).

What are some tank maintenance tips?

Always use specially formulated RV holding tank chemicals to ensure your tanks stay odor-free and that waste is broken down quickly and effectively. While you can use mild dish detergent or ice to clean your tanks more thoroughly, avoid using harsher substances, like antifreeze, which can dry out the seals and ruin your sewer system.

Does my toilet use affect anything?

Your RV toilet isn’t like the one you have in your home! Flushing trash, feminine products, and non-quick-dissolve toilet paper can lead to a clog in no time, and it’ll be no fun to clean up. Treat your toilet with care and only flush the bare necessities. That way, it’ll be there for you for many camping trips to come.

This post may contain affiliate links.

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