How to Clean Out an RV Black Water Tank (5 Simple Steps) (2023)

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 blackwater tank is the equivalent of a home’s septic tank, and a lack of cleaning will lead to its content’s stink wafting back into your RV.

Even worse, a neglected tank can lead to plumbing issues and breed dangerous bacteria that could harm you.

Luckily, deep cleaning your black tank doesn’t have to be tedious and 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, protect yourself by wearing rubber gloves and protective glasses. Shoe covers and a face mask are optional but 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
We 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 campsite or dump station. 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 tanks. Continue below for written step-by-step instructions

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: Use an RV sewer hose support system to create a downhill effect for your hose. This will help for sites where the ground slopes uphill to the dumping sewer inlet.

3) Open the black tank valve to empty it.

4) Once it’s empty, open the grey tank valve and let its water 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, and other problems.

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, or two cups of liquid bleach into the tank via the toilet.

Note: Contrary to popular opinion, bleach, when used correctly, 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

Flushing is a thorough cleaning process that eliminates all waste from the black tank’s walls and floor with pressurized water. We recommend flushing your tanks after every camping trip.

Depending on your RV’s design, you can flush the tank with the built-in flush port, a handheld backwasher, or a removable black tank rinser.

Using the Black Water Tank Flush Port

1. After your black tank is completely empty, locate the flush port on your RV. It’s typically located on an outside wall next to the city water connection. Consult your owner’s manual if you are having trouble locating it.
2. Connect a standard garden hose to the flush port and a nearby water source. Do NOT use your RV’s freshwater hose for this purpose, as you don’t want to potentially contaminate your fresh water supply.
3. Before turning on the water, ensure your black tank valve is open.
4. Turn on the water at the spigot and let it run through your black tank and out your sewer hose for 2-3 minutes or until all of the water coming out is clear. This is where having a clear sewer hose adapter comes in handy.
5. Turn off the water and disconnect the garden hose. You’ll notice the water will continue draining out of your sewer hose for a few minutes. Once that is done draining, close the black tank valve.
6. Disconnect the sewer hose and replace the cap on your holding tank outlet.

Using a Handheld Backwasher

Most handheld systems come in the form of a wand that you can stick down the toilet to pressure wash the tank. To use the wand:

• Attach it to a water hose that’s plugged into a tap
• Close the tap until the wand is down the toilet
• Once the wand is in the tank, open the tap
• Move the wand around the tank to pressure wash every possible corner
• Keep going until the waste passing through the clear hose adapter is debris-free

How quickly and effectively you can do the job with a handheld backwasher will depend on the product’s quality. We recommend the Camco Flexible Swivel Stik.

Using a Black Tank Rinser

If your rig doesn’t have a flush port, you can opt for a holding tank rinser, which connects between the holding tank outlet and your sewer hose.

Once installed, you simply connect a garden hose to this device, and it creates a high-flow blast of water in through the sewage pipe and into the tank.

I personally prefer this method over a handheld backwasher.

Step 5: Prepare the Tank & Toilet

The last 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 the dreaded poo pyramid and make the tank 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 will cause clogging issues later on.
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. You can get it as a liquid, tablet, pouch, or powder to suit your preference.

Final 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 that will help you avoid costly mistakes and make the process go a little smoother.

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 rinser that can bend to enter the tank at an angle.

Products Mentioned in This Guide

• Rubber gloves
• Protective glasses
• RV sewer hose support
• Camco 90 Degree Sewer Hose Adapter
• Camco RV Flexible Swivel Stik with Shutoff Valve
• Camco Rhino Blaster Sewer Tank Rinser with Gate Valve
• Bio-Pak Natural Holding Tank Deodorizer and Waste Digester Drop-Ins