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RV Black Tank Flush: What It Is and How to Use It

The #1 rule of RV black tank dumping is to empty the black tank first, followed by a cleansing rush of the gray tank’s contents. However, your black tank isn’t “clean” at the end of that process. Not unless you flush your RV black tank.

The good news is that you may have an RV black tank flush feature that makes this step easy. The trouble is, you might not be aware that it’s there or of how to use it. We sure didn’t when we first started RVing! If you don’t have a tank flush feature, we’ve also got you covered.

What Is an RV Black Tank Flush? 

An RV black tank flush is a system designed to clean out the black water holding tank in a RV camper. The black tank is where waste from the toilet goes. Over time, solid waste and toilet paper can build up in the tank, leading to unpleasant odors, potential clogs (aka the Poo Pyramid), and inaccurate sensor readings.

The black tank flush system typically consists of a connection on the outside of the RV that you can attach a hose to. Inside the tank, there are sprayers or jets that spray water at high pressure throughout the black tank. When you connect a hose to the flush system and turn on the water, these jets help to break up solid waste and clean the tank’s interior walls.

Pro Tip: New to RVing? Be sure to read the RV Black Water Tank Survival Guide.

RV Black Tank Flush
As the name suggests, an RV black tank flush helps flush out and clean your wastewater tank.
RV black tank flush location
The RV tank flush should be labeled or located near the black tank valve

Where Is the RV Black Tank Flush Located?

In some RVs, the black tank flush hose connection is above the dump valve. You should mark it with the words “Black Tank Flush” if it is not already.

In other RVs, the black tank flush is on the opposite side of the dump valves. You should also mark this “Black Tank Flush.”

Some RVs have three hose connections very close to each other, so you’ll want to pay careful attention to their identification. They’re probably called “City Water,” “Winterization,” and “Black Tank Flush.”

black tank flush location
On this RV the tank flush is the black connection however it is not labeled. Consult your owner’s manual if you are unsure.

How to Use Your RV Black Tank Flush

There are two primary ways to flush your black tank. Both will do the job; however, the advanced method will give you a more thorough clean. Let’s take a look at the steps involved in each method.

Simple Cleaning Method

Step 1: Empty your black and gray tanks as usual.

Step 2: Then, with your black tank dump valve OPEN, connect a hose from the water source to your RV black tank flush inlet. 

Step 3: Double-check that your black tank valve is OPEN!

Step 4: Turn the water on, and the black tank flush will rinse/flush out your black tank. 

It’s that simple!  

rv black tank flushing
Using your RV black tank flush is relatively simple but has big payoffs.

Advanced Cleaning Method

If you want to go the extra mile and get the tank even cleaner you can follow the advanced cleaning procedure.

Step 1: Empty your black and gray tanks as usual.

Step 2: With your black tank dump valve CLOSED, connect a hose from the water source to your RV black tank flush inlet. 

Step 3: Have someone inside open the toilet bowl and look into the empty black tank.

Step 4: Start a timer and turn the water on, and let the black tank fill up with clean water.

Step 5: Have the person inside tell you when the tank is near full and turn off the water. Stop the timer at the same time.

Step 6: Open the black tank valve and rinse out the tank with fresh water.

Step 7: Set a timer for shorter than when you saw your tank fill and repeat the process, opening the tank when the timer goes off. Repeat until clear water runs out of the tank.

The advanced cleaning will do a much better job of getting the tank flushed.

WARNING: IF YOU FORGET TO TURN OFF THE WATER, YOU WILL HAVE A SEWER EXPLOSION IN YOUR RV OR EVEN OUT THE VENT VALVE ON THE ROOF! DON’T LEAVE THE TANK CLOSED WITH THE FLUSH ON TOO LONG.

Clear sewer hose elbow
It may be gross, but the clear elbow will help you know when your tank is clean.

Tips for Using Your RV Black Tank Flush

Tip #1: Use a transparent elbow on your sewer hose connection so you can see when the water runs clear.  

Tip #2: Make sure you have the dump valve OPEN when you flush the tank so the toilet doesn’t overflow inside your rig! If following the advanced cleaning method, always set a timer, and do not forget to open the valve!

Tip #3: Stay nearby while flushing your black tank. Keep a close eye on the process.

Tip #4: Don’t leave the hose connected to the black tank flush when not in use because someone might turn on the hose with the black tank valve closed. (Don’t ask us how we know this.)

Cleaning the Tank Without the Flush System

While most RVs these days have a black tank flush, some do not, or it may not work. In this case, you still must flush the tank another way. Our personal RV did not have a working flush for years, but we were able to keep the tank clean.

In this case, it’s best to clean the tank through the toilet. Most RVs have a gravity flush toilet that connects directly to the tank. What you will do in this situation is run a hose into the RV’s bathroom. Open the toilet and spray water into the tank. You can use the same advanced method above of filling the tank, then opening the valve to flush it. This works just as well as the tank flush but requires a little more effort to run the hose into the RV.

If you want to be able to spray around the edges of the tank with the valve open, you can also purchase special tank cleaning wands. These connect to the hose and spray water at a 90-degree angle once inserted into the toilet.

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What If the Flush Did Not Fix My Sensor Issue?

It is possible that over time some harder deposits will form in your black tank. “Struvite” is what we call some of these unavoidable deposits. They are crystallized and need much higher water pressure to be removed. In this case, you will need to have your tanks professionally power washed. The video below showcases how this is done.

Struvite is a type of mineral scale that accumulates on the inside walls of tanks and pipes. It can slow drainage and contribute to the poor functioning of tank sensors. 

If you purchased a used RV and have tank sensor or drainage issues, struvite buildup may be the culprit, especially if the RV is relatively old. 

Pro Tip: Does your RV toilet still smell bad after flushing your black tank? Here are the top Reasons Why Your RV Toilet Stinks.

RV Holding Tank Sensor Fail! Power Washing Black & Gray Tanks & Struvite Removal.

How Often Should You Flush Your Black Tank?

Flush your black tank every few times you dump it as a matter of routine. Should you find that your sensors are not reading correctly, running your black tank flush might clear up the issue. If not, you may want to consider putting some black tank cleaner or even just add some Dawn dish soap in the tank to help break down some of the sludge. Worst case, having a professional conduct a true powerwash of the tank to remove the struvite buildup on the tank’s sides. 

In most other cases, regularly using your RV’s black tank flush will lessen the likelihood of these issues developing.

Now that you know where to find your RV black tank flush and how to use it, you can give your black tank an enema now and then to keep it clean and well-functioning. 

Just remember to open that dump valve or set a timer! 

Is your RV toilet malfunctioning? It’s likely an easy fix! Find out: What Are the Parts of an RV Toilet & How to Replace Them

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About Tom Morton

Tom, a Pacific Northwest native, is our technical genius. Born in Washington and raised in Alaska before settling in Michigan. He's the man who keeps our operation running, both figuratively and literally.

With a background in Electrical Engineering, Tom specializes in RV solar systems and lithium batteries. He made history as the first documented individual to use a Tesla battery module as an RV battery. Tom has personally assisted countless RVers with system installations and has educated thousands more through his videos and articles.

Cinematography is another of Tom's passions, showcased in his work on the Go North series. You can see his camera skills on display in The RVers TV show on Discovery Channel and PBS where he also stars as a co-host.

Tom's mechanical expertise extends beyond RVs to boats, planes, and all things mechanical. He's renowned for taking on maintenance and repair projects single-handedly and is often spotted underneath RVs, making him the technical backbone of our endeavors.

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Gilles Mercier

Saturday 13th of January 2024

Good morning team. About black tank sensor accuracy problem, a good way to accelerate deep cleaning process, is to use ice cubes added in black tank with few gallons of water, just before you're leaving your camping site. So, water will run ice cubes again walls of black tank an rub all souffleuse on the walls. It work ! We did it 3 times on our 2014 rv trailer with great success . Thanks for all your tips and infos.

The Mortons

Sunday 11th of February 2024

Thanks for your tip Gilles!

Meg Magruder

Monday 5th of June 2023

We are having an issue with the sensor on our gray tank. We are a very water stingy when RVing and maybe put 2-3 gallons in the gray tank on each RV trip. mostly hand washing dish rinsing. We have been trying the dishwasher soap, but it is consistently 3/4 full on the inside display.

Matt Greven

Tuesday 18th of October 2022

Love your channel! I'm only about 13 months into ownership. One of the things suggested to me on a Tiffin FB group was to use a water flow-meter when connected to the sani-flush fitting. I ALSO have an observer inside--just to make sure!

David Cox

Wednesday 28th of September 2022

Yes, I'm "one of those people" who didn't realize we had a flush valve in our RV. The flush was easy and effective. Thanks Mortons!--DC

Mortons on the Move

Saturday 1st of October 2022

Glad you found it and were able to flush your tank easily! :)

LE

Wednesday 23rd of February 2022

I love that you have a bidet, I was wondering if that would work in an RV. Is that a normal household bidet or something special to RVs?

Mortons on the Move

Monday 14th of March 2022

Its a normal type that connects to the seat cover. Its going to depend on your RVs toilet however so measure the seat lid bolt hole spacing.