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

Do you follow the #1 rule of RV black tank dumping? That is emptying the black tank first, followed by a cleansing rush of the gray tank’s contents? Great! Think your black tank is clean at the end of that process? It’s not unless you use an RV black tank flush. 

The good news is that you may have an RV black tank flush that goes the extra mile in keeping your black tank clean. The trouble is, you might not be aware that it’s there or of how to use it. If you don’t have a black tank flush then what? Let’s learn about cleaning out your black tank now! 

What Is an RV Black Tank Flush? 

The RV black tank flush might be part of some rigs’ tank systems, but it’s a bit of an enigma. You see, many RV owners aren’t even aware that the system is in place, but a black tank flush can be beneficial for a couple of reasons. 

The first reason is obvious–we want to keep the black tank well maintained. Why? Well, let’s just say no one likes to deal with black tank issues! We don’t want a leak, a drip, a malfunction, and goodness knows, we don’t want a smell throughout the RV!

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

But there’s another reason to flush your black tank well. It has to do with the panel sensors inside your RV that tell you when the tank is full. 

We can all agree that knowing our black tanks’ status is essential to trouble-free RVing, toilet edition! But when our tank sensors aren’t delivering the information, there’s no way to know the tank’s capacity. Unless you’re a fan of opening the toilet drain and peering closely to get a good look at its contents. (Don’t drop that flashlight!)

Many RVers are not aware that the black tank sensors can become “gummed up” with sludge (Yeah, we’ll just call it “sludge.”), despite the tank being dumped and the hose being flushed with gray water regularly. Here’s where your RV black tank flush comes into play.

How Does a Black Tank Flush Work? 

If your RV is so equipped, you can use your black tank flush to thoroughly rinse the tank once you’ve emptied it. When you connect a water hose to the inlet valve, it will “powerwash” the tank’s interior. 

The inlet hose connects to a nozzle inside the black tank that has small holes to spray water all around the tank. Sometimes these nozzles even rotate, but many of these types will eventually fail.

This process helps to remove “stuff” left behind after the general dumping process. And yes, “stuff” is left behind.

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.”

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!  

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.

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 RV’s these days have a black tank flush, some do not, or it may not work. In this case, the tank should still be flushed. 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.

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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