Wednesday, March 29, 2023


Problem: “Poop mountain” forms in black tank

This reader question was answered by RV technician Chris Dougherty when he served as the technical editor of

Dear Chris,
We’ve been stationary for almost a month, so far. I’ve noticed what I think is a pyramid formed at the pipe base in the black tank. This has occurred twice in two weeks. I use one of those magic wands to clear it. We use probiotics in all tanks and Scott toilet paper. I use the flush king after every emptying. Any thoughts or suggestions? —Alan

Dear Alan,
This is a common problem, and you’re fortunate that you can actually see into your tank, as many RVers can’t. The problem is a result of too little water in the black tank. This can be an RVer’s error, or it can be a malfunction.

When it comes to sewage, water makes the world go ’round… and the sewage go down. For some people, they use no extra water in the holding tank because they are afraid to fill it up too quickly, especially if they’re dry camping. Others, especially if they’re on a seasonal site, leave the black tank valve open all the time, thinking everything will just drain, and it doesn’t…causing a buildup of sludge. Some folks won’t use chemicals, which can also do the same thing.

From the malfunction standpoint, the black tank system could have a leak. It could be as simple as a poorly sealing termination valve, or it could be more serious, like a cracked tank, or a failed pipe connection at the tank. If the tank has failed, there will be signs of leakage and odor. If your unit has an enclosed underbelly, there should be staining where the liquid has drained, and sometimes pooling which will weigh the underbelly enclosure down causing it to bow.

Finally, if the leak is in the valve, and this is the most common malfunction, it will be obvious when the cap is removed from the termination to dump the tank after use. If you are leaving your hose connected all the time, then there will be no sign of this, of course.

This is often caused by one of a couple of things: there is some stuff jammed in the o-ring part of the valve, the o-ring has failed, or the valve is in need of lubrication to make it close properly.

The best way to fix this is to service the valve, especially if it has been in use for a long time. To do this, disassemble the valve, clean the parts, replace the seals (available on Amazon), reassemble and lubricate using Dow Corning 111 valve lubricant.

Hope this helps!




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3 years ago

Try using RV DIGEST-IT. Made by Unique RV products.

Liquid or Drop In packs. I use the liquid. It is an enzyme based, Non-Toxic product and it does break down all type of toilet paper.

Keeps the tank clean and have not had a problem to date.

I used to use HAPPY CAMPER Powder. However, it did not work as good as RV DIGEST-IT!

What many people don’t realize is most toilet chemicals offered by Dometic and Thetford are really nothing more than DEODERIZERS, (makes your poop smell better) . They do very little to help break down waste. You need a product in your tank to help breakdown waste. AND USE LOTS OF WATER! WATER IS YOUR FRIEND. Between my Wife and me, we usually get about 4 days use (40 gallons), before needing to dump.

And make sure your BLACK TANK VALVE IS CLOSED! Again, the number of RVers that leave their valves open is amazing and then they wonder why they have problems!

Glen Wells
3 years ago

Any sewer problems can be fixed by happy campers Canada. Multiple uses from the product and a money back guarantee!

3 years ago

We just did this. We bought a 5 gallon of degreaser simple green at home depot ,like 25$ and put 1/4 water in and let it sit for 2 days. Did a good job loosening up all the deposits. We dont put any toilet paper in the tank though, so that might make a difference .

3 years ago

I like to use 1cup dawn & 1cup of calgon water softner in 2 gallon water cleans tank & no odor

3 years ago

after dumping, I typically put 10gal of fresh water in my tank (along with the orange liquid) so it will slosh around on the drive home and break up anything that didn’t come out when the tank was flushed. It also affords any “leftovers” time to break down before the next time. This leaves the tank fairly “clean” when I arrive at the next destination. (the crappy tank level indicators from Keystone still don’t read but it’s an 80gal tank and I can’t imagine ever filling it with only 2 people.

3 years ago

You can try using a product by Unique! Called “RV Digest-IT”! An enzyme based product that breaks down waste into liquid! Works Great, and helps to keep your black tank Clean! You can also use it in the Grey tanks as well!

Good product!

RV Staff
3 years ago
Reply to  Jeff

Thanks, Jeff. Yep, we like RV Digest-It at That’s why we advertise it in our newsletters: 😀 —Diane at

Paul C Huff
3 years ago
Reply to  Jeff

I’ve used RV-Digest-It for about ten years. I’ve NEVER had a problem! It is a great product!!

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