How to Clean Out an RV Black Water Tank (5 Simple Steps)

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If you haven’t thoroughly cleaned your RV’s blackwater tank, all the air fresheners in the world won’t hide the bad smell.

That’s because a black water tank is the equivalent of a home’s septic tank, and a lack of cleaning can lead to plumbing issues and unpleasant odors filling your RV.

Luckily, deep cleaning your RV’s black tank doesn’t have to be tedious or messy with our simple 5-step plan!

Step 1: Prepare for the Job

Your black tank’s contents are hazardous, so you should avoid inhaling any fumes or letting it get on you or your clothing.

Before you start cleaning, I recommend wearing rubber gloves and protective glasses. Shoe covers and a face mask are optional but also recommended.

Just in case, have soap and running water nearby for cleaning up after the job.

Tip: Avoid bringing contaminants into your RV by cleaning up outside.

Step 2: Empty the Tanks

Once your protective gear is on, the first step in the cleaning process is emptying the RV tanks.

Quick Tip: When to Empty Your RV Holding Tanks
I recommend emptying your tanks before they become too full, or the excess content might damage the tank or plumbing and lead to your black tank leaking. However, make sure your black tank is at least 2/3rds of the way full. Emptying your tank too often can leave solid waste behind. When it’s near full (between 2/3 and 3/4 full), it’s easier for the solids to break down and empty.

Once it’s time to empty your tanks, park your RV near the dumping inlet, which you’ll find at a dump site. If you are emptying the tank at your house, check out our guide on how to dump an RV black tank at home.

Here’s a quick and concise video on how to empty your wastewater tanks. Continue below for written step-by-step instructions

Dumping your RV's Black and Grey RV Water Tanks

Watch this video on YouTube.

1) Pull up to the dump station as close as you can to the dump station inlet

2) Hook your sewer hose to your RV and then to the dump station inlet. The bayonet-style end goes in your RV, while the “L” shaped elbow end will go in the dump station inlet. Check out our guide on how to properly hook up a sewer hose for more information.

Tip: Before proceeding to the next step, let a small amount of gray water run through the sewer hose first. This does two helpful things. First, it lets you confirm the hose is connected properly and that there are no leaks before the black tank starts draining. Second, that little bit of soapy gray water can help wet the inside of the hose before the heavier black tank waste comes through. Do not drain the whole gray tank yet. Just open the valve briefly, check your fittings, then close it again.

3) Open the black tank valve to empty it.

4) Once it’s empty, open the gray tank valve. This allows the contents of the gray water tank to flush the sewer hose clean.

To avoid running into trouble with other campers while draining your black tank, stick with these tips:

• Be polite to others at the dump station. Unruly behavior has led to the closure of dump stations across the country.
• Don’t use harmful chemicals like formaldehyde to flush your waste tanks. It damages your tank and equipment at the dump station.
• Close the black valve until you are ready to dump and again immediately after dumping is complete.
• Don’t use the RV’s drinking water hose to flush the black water tank or sewer hose. Using it for such purposes can contaminate your fresh water source.

Step 3: Soften and Remove Waste Tank Buildup

Removing waste tank buildup is something you should do at least once a week. If not, the waste can cake to the side of the tank, causing blockages, odors, issues with tank sensors, and other problems (like your RV toilet smelling when you flush).

After emptying the waste tank, lock the drain outlet and begin the buildup removal process by flushing the toilet until 3/4 of the black tank is full.

Next, we simply need to use your black tank treatment of choice, whether a liquid enzyme cleaner, homemade holding tank treatment (like the Geo Method), or two cups of liquid bleach into the tank via the toilet.

Note: Contrary to popular opinion, bleach will not hurt your tank or plumbing when diluted and used correctly. Be sure not to let the water/bleach mixture sit for more than 10 minutes and completely rinse out the bleach.

Give the mixture 10 minutes (no longer) to soften the caked waste within your tank and sterilize it. After 10 minutes, drain the tank’s contents and fill it with water before emptying it again.

If using bleach, keep doing this until the bleach smell completely disappears and you can’t see debris passing through the clear hose adapter. Making sure the bleach smell is gone ensures no bleach residue damages your plumbing or tank.

If you regularly perform this step (weekly), then more often than not, your tank will be thoroughly cleaned out, and you can skip ahead to step 5. However, if you still have buildup in your black tank, you will need to flush it, as described in step 4.

Step 4: Flushing the Black Water Tank

Dumping the black tank can leave paper and waste behind. Rinsing helps remove that material before it dries. I recommend rinsing after every camping trip.

You can pour water through the toilet, use a built-in flush port, or clean with a toilet wand or external backflush attachment. How well each method works depends on your tank’s shape, plumbing, and where the water reaches.

Clear water coming through the sewer hose doesn’t prove the tank is clean. Tests using a tank with a clear lid showed heavier debris remaining inside even after the water looked clear. A clear sewer adapter helps you see what’s coming out, but it can’t show everything left behind.

Pouring Water Through the Toilet

A bucket of water is a simple option worth trying. In this comparison of two black tank cleaning methods, rapidly pouring about five gallons through the toilet opening stirred up heavier material that two complete backfill-and-dump cycles had left behind. A second bucket removed more.

1. Drain the black tank, leaving the sewer hose securely connected to an approved sewer inlet and the black tank valve open.
2. Fill a bucket with clean water. Use an amount you can comfortably lift and control.
3. For a conventional RV toilet that drains directly into the black tank, hold the toilet valve fully open and pour the water briskly through the opening. Avoid splashing or pouring faster than the toilet can accept it.
4. Let the water drain, then repeat if needed. Keep the sewer hose connected until all rinsing is finished.

The bucket method in that test used an open drain, rather than filling the whole tank and then opening the valve. It also came after two backfills, so the test doesn’t prove a bucket alone will outperform every other method. Toilet placement and bends in the plumbing can change the results. This procedure isn’t intended for macerating or vacuum toilets.

Using the Black Water Tank Flush Port

A built-in rinser can help wash residue from the walls its spray reaches. However, this flush-port rinser test showed that larger clumps and some stuck toilet paper remained after rinsing. Five minutes cleaned more than one minute in that setup, but longer rinsing brought smaller improvements and still didn’t remove everything.

1. After draining the black tank, leave the sewer hose connected and locate the labeled black tank flush port. Check your owner’s manual if you’re unsure which connection to use.
2. Connect a hose reserved for tank rinsing to the flush port and an appropriate water source. Do not use your drinking-water hose.
3. Keep the black tank dump valve open while operating the rinser, and follow your RV manufacturer’s instructions for water pressure and use.
4. Turn on the water and stay with the RV throughout rinsing. Watch the discharge through a clear sewer adapter to see what is coming out, without treating clear water as proof that all debris is gone.
5. Turn off the water, disconnect the rinse hose, and let the remaining water drain. Close the black tank valve once you’ve finished all cleaning steps.

If you already have a built-in rinser, use it to help wash down the tank. Just don’t expect its spray to reach every area or remove dried buildup on its own.

Using a Toilet Cleaning Wand

A toilet wand lets you direct water into the tank through the toilet opening. Check that the wand suits your toilet’s plumbing before using it. A straight drop provides easier access than a pipe with bends, and even a flexible wand may not work with every layout.

• Leave the sewer hose connected and the black tank drain valve open.
• Attach the wand to a dedicated rinse hose, keeping its water control shut off until the wand is positioned.
• Hold the toilet valve fully open and carefully insert the wand according to its instructions. Don’t force it through bends or against the toilet seal.
• Turn on the water and direct the spray toward the areas you can reach. Watch the discharge for loosened material.
• Shut off the water before removing the wand, then let the tank finish draining.

The Camco Flexible Swivel Stik is one option. Its usefulness depends on access through your toilet and how much of the tank the spray can reach.

Using an External Backflush Attachment

An external backflush attachment connects between the RV’s holding tank outlet and sewer hose. It sends water backward through the drain plumbing. Some models include a gate valve that allows you to add water to the tank before draining it again.

Don’t assume that water entering through the outlet will pressure-wash the whole tank. Bends and distance between the attachment and tank can limit where the stream reaches. In the bucket comparison above, backfilling moved some floating paper but left much of the heavier material on the floor.

Follow the attachment’s operating instructions, use a dedicated rinse hose, and stay beside the controls whenever water is flowing. If you’re adding water with the attachment’s valve closed, monitor the fill closely and stop well before the tank is full. Don’t rely only on a tank monitor that may give inaccurate readings.

Step 5: Prepare the Tank & Toilet

The final step is preparing the toilet and black tank for use until the next clean. This entails adding water and an enzyme cleaner to your black tank.

Do NOT skip this step! This is the most important thing you can do to prevent a poop pyramid in your black tank and make the cleaning process as simple as possible the next time.

1. Fill the tank about 10% with water. You can do this with a 5-gallon bucket or by flushing the toilet four to five times to fill the black tank’s bottom. If you don’t do this, the first waste that goes in will solidify and stick to the bottom, which could make your RV black tank clog up.
2. When there’s enough water, add an eco-friendly enzyme cleaner.

Enzyme cleaners use macromolecular biological catalysts (enzymes) to accelerate the breakdown of waste. Aside from liquefying waste to prevent clogs, enzyme cleaners also prevent odors. These benefits will work together to make your next black water tank cleaning easier.

Also, unlike products that contain formaldehyde or other harsh chemicals, enzyme cleaners don’t damage water tanks or other aspects of your plumbing system. You can get it as a liquid, tablet, pouch, or powder to suit your preference.

Alternatively, you can just use a little Dawn dish soap in your black tank to help keep it clean between dumpings.

Tips for Cleaning an RV Black Water Tank

We covered everything you need to know about cleaning out an RV’s black water tank. But there are a few more tips we’ve learned over the years through experience that will help you avoid costly mistakes and get the best results.

Leave the Sewer Hose Connected

During steps 2, 3, and 4, your black tank drain must remain connected to the sewer drain. If not, you could end up with a nasty mess on the ground (or worse, on you)!

Use a Clear Sewer Hose Adapter

You also will want a clear sewer hose adapter. Without one, the only way to see how clean the tank is during each flush is by opening the drain line while waste flows out of it. You don’t want that.

Pick the Right Handheld Backwasher

If using a handheld backwasher, consider your toilet’s design. Straight tank rinsers are suitable for toilets with black tanks directly beneath them. If the tank isn’t directly under the toilet, go for a flexible tank wand that can bend to enter the tank at an angle.