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What is a Black Tank on an RV?

A black water tank on an RV is a specific type of water holding tank that is used to collect and contain human waste. These tanks are generally installed in the undercarriage of an RV and essentially serve as a septic tank for your camper.

what is a black tank on an rv

Table of Contents

How Does a Black Tank Work?

Only RVs with toilets have a black water tank. When you flush your camper’s toilet, the water, and human waste flow together into the black water holding tank.

This process repeats every time you flush your toilet, letting the waste collect in the tank until you can empty it at a dump station.

RV toilet

Dump Stations

A dump station is an ordained location to dump the waste out of your black water tank. You can almost always trust that an RV campground is going to offer the option of dumping your black tank waste.

Typically, this service is included in the price of staying at the RV campground. You can also sometimes drive into the park and dump your waste for a small fee, without having to stay overnight.

Aside from RV campgrounds, search for dump stations at gas stations, rest areas, and truck stops. Occasionally you may be able to find a dump station provided by the city, but these aren’t as common.

How to Empty Your RV Black Water Tank

Depending upon the size of your black water tank, you will find yourself needing to visit a dump site every 5 days to a couple of weeks.

To empty your waste, first, find a proper black water dumping station. NEVER dump your black tank out in nature or anywhere other than a proper dumping station. Releasing human waste into the environment is harmful to the health of animals, plants, and other people.

Next, connect your wastewater hose to the black water tank valve. A wastewater hose is a flexible hose, roughly 4 inches around, that is used solely for the purpose of dumping your black tank.

After connecting the wastewater hose to your RV’s black tank valve, connect the other end to the dumping station port. Open your black tank valve and allow the black water and human waste to flow into the dump station.

Empty RV black water tank

You should be able to hear, and if you have a translucent hose even see the waste flowing from your holding tank into the dump station holding tank. I would suggest not watching or listening to it for too long because it’s gross.

Immediately after dumping their black tank, many people choose to drain their grey water tank as well. This is because the wastewater from the grey tank will serve to clean extra bits of solid waste out of the waste hose, minimizing how much you have to manually clean the waste hose.

Note that a grey water tank and black water tank have very different functions in your camper. We’ll get into that more in a bit.

Maintaining the Health of Your Black Tank

A camper’s black water tank needs regular maintenance and attention to function properly. There are several tasks you can do consistently in order to prevent unnecessary damage or clogs in your black tank system.

Add Water

null throughing water

Before the start of your next RV adventure, pour a gallon or two of water into your black tank via your toilet. This step may seem counterintuitive because adding water will take up valuable black tank space, right? Technically yes, but by doing this step you will avoid what is known as “the mountain of poo”.

This glorious term refers to when solid waste builds up in a black water tank, forming a gross pyramid of waste that grows until it impairs the function of your toilet flusher. Nobody got time for that.

Adding water to your tank allows the solid waste to disperse evenly as it collects in the tank. A larger Class-A RV with a large black tank will need two, maybe even three gallons of water to accomplish this. Smaller class-B motorhomes and converted vans will only need about a gallon.

Add Treatment Chemicals

Another way to avoid the mountain of poo and stay on top of tank maintenance is to add enzymatic chemicals to your RV’s black tank. Adding these chemicals should be done at the start of your trip, typically at the same time, you add the water to your RV black tank.

Similar to how stomach acid works in a stomach, these chemicals break down solid waste and toilet paper as it is collected in the tank.

Breaking down the solid waste not only avoids everyone’s least favorite mountain but also aids in a smooth dumping process and mitigates the odors produced by your RV black tank.

Clean Regularly

Cleaning out your black water tank seems like the type of task that could be pretty involved and nasty. In reality, it’s a fairly simple process that can be done with very little mess, if done regularly. I suggest doing this after every trip to ensure you avoid clogs.

water pipes RV

Follow these steps to quickly and easily give your black tank a washing:

  1. Drain all liquid and solid waste from your tank at a dump station
  2. Fill the tank back up 1/2 full of fresh water
  3. Add a biodegradable soap such as Dr. Bronner’s or Simple Green into your black tank
  4. Drain your tank into the dump station
  5. Fill the tank back to 1/2 full and drain again.
  6. Repeat filling and draining until water draining out tank runs clear

If you do this frequently, you should manage to keep your black water tank free of clogs and the buildup of nasty odors.

How to Tell When Your Black Tank is Full

The tank sensor is the most common way you will check to see how full your RV black tank is. A tank sensor should be installed in the freshwater tank, grey water tank, and black tank of your RV. These sensors serve to give you a reading on how full your tanks are, allowing you to know when to head to a dump station and dump your tanks.

Occasionally your black tank sensor might be faulty, or your tank might simply not have a sensor. In these instances, you will need to listen for the tank to “burp” when you flush. This “burp” is a small release of air from your toilet when you flush and is indicative of needing to drain your black tank.

You should quickly develop an ear for the tank burp after you’ve traveled in your RV for a while.

How Often You Should Empty Your Tank

This will depend on a variety of factors:

  • Amount of people are staying in your RV and using the toilet
  • Your frequency of using RV toilets over toilets provided at RV campgrounds
  • How much water do you use during each flush
  • Whether or not you flush toilet paper

Because each of these variables will change from person to person, the frequency at which you have to dump your tanks will be unique to your camping style.

Difference Between Grey and Black Tanks

The grey and black water tanks in your RV are the two waste tanks used in your RV’s plumbing system. We already know what the RV black water tank is, so what is a grey water tank?

A grey tank collects the water that drains from your faucets and shower in your RV. The water collected in this tank is typically water that has been used for cleaning dishes, food, and bodies.

RV cleaning

It is referred to as the grey tank because the water collected in it usually has a greyish hue to it, whereas black tanks contain much darker water. While the RV black water tank acts as a septic system, the grey tank is just a temporary storage container allowing you to avoid dumping wastewater into the environment.

You’ll likely find it convenient to empty your tanks at the same time, saving some time and gas as you commute to the dump station.

Tips and Tricks for Black Tank Use

Flush Lightly

When flushing, don’t hold down the flushing handle for too long. This will allow you to use as little water as possible for each flush, and lengthen the time between dumping your tanks.

Use Safe Toilet Paper

Not all toilet papers are created equal. Septic safe toilet paper refers to toilet paper that breaks down quickly and doesn’t contain bleach or other chemicals that could be harmful to your RV black water tank or the environment.

RV toilet paper

Many big brands sell septic-safe toilet paper. Just be sure to carefully read the labeling to ensure you’re flushing the right stuff into your tank.

Use Less Toilet Paper

Try using as little toilet paper as possible for every wipe. Realistically most people use far more TP than necessary and doing so could severely clog your RV black water tank if it is not breaking down solid waste well.

Instruct small children and guests staying in your RV on the proper amount of toilet paper to use for every trip to the bathroom.

Only Flush Waste and Toilet Paper

Never flush anything except human waste and toilet paper into your black water tank. Tampons, pads, condoms, and other types of trash need to be disposed of in a separate bin in your RV bathroom.


Some RVers take this one step further and also throw used toilet paper away in a bin instead of flushing it. This might seem gross if you were raised in a country where this isn’t common, but it is actually a common practice worldwide and fairly easy to get used to.

Keep Valve Closed

NEVER keep your black water tank valve open in between dumping. It is illegal in some areas and is just plain disrespectful to the environment and others. Always close your black water tank valve after each dump.


A clean, personal toilet is a small pleasure while out adventuring in nature. Now that you’ve learned a thing or two about maintaining your septic system, you will always be able to rely on your RV toilet and black water tank to do their jobs.

Happy pooping!

About Author
About Author

Schuyler has been working and playing outdoors his entire adult life. As a ski-bum in his early 20’s, he began building campers in the beds of pickup trucks to pursue a life of freedom and adventure. After a decade of experience as an artist and carpenter in Washington State, he moved to Colorado to work as an RV technician, converting vans into luxury campers. Now he is traveling the world, using writing as a way to continue his passion for creativity and artistry.

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