How to Get Rid of Black Tank Buildup

We’re going to talk about the dreaded black tank and black tank buildup today. It’s just a fact of RV life that can’t be avoided. The black tank is where human waste is held until it is emptied. My black tank’s capacity is 38 gallons. That’s fairly average-sized in the RV world. Those big rigs you see on the road and in the campgrounds can have upwards of 80 gallons capacity. Take a moment to visualize that!

Problem – black tank buildup

Living in my Airstream full-time means sometimes I’m stationary for extended periods of time. Last December, when I was moochdocking in my daughter’s driveway I use a macerator and two dedicated, hunter orange, garden hose-sized hoses to pump out the holding tanks. I was there for several weeks and over that time my black tank began to develop a layer of waste on the bottom that I couldn’t get out no matter how hard I tried.

This post is my test and review of Unique Camping and Marine Holding Tank Cleaner. Unique is formulated to treat the problems in the image below.

black tank

For more in-depth information about your RV holding tanks, see All About RV Holding Tanks below.

Everything You Ever Wanted to Know About RV Holding Tanks

The black tank sits directly beneath my toilet and you can actually push down the flush pedal and see right into the tank. Gross, I know but sometimes you need to know what’s going on in there. If you just flushed the tank and you can’t see the bottom, you have some black tank buildup. Buildup can also occur on the sides of the tank and that causes your tank sensors to read incorrectly.

Normally, flushing your black tank is done through a three-inch hose and there is a lot of force because the tank is nearly full. When I use the macerator, I don’t have the assistance of the force of the full tank or the large sewer hose.

Why is Black Tank Buildup a Problem?

Black tank buildup is not terrible in itself but it can cause additional odor and tank level sensor malfunctions. If left unchecked, it can also eventually completely block your tank’s outlet causing it not to drain at all.

What didn’t work

When I left my daughter’s driveway for my winter trip added a cup of Dawn dishwashing liquid and some hot water then sloshed my way down the highway in an attempt to break up the layer that had formed in the tank. It helped some, but I could never get that black tank buildup out, even after driving several thousand miles.

Unique black tank cleaner to remove black tank buildup

The solution – Unique RV Black Tank Cleaner

I saw an advertisement for a professional-grade black tank cleaner with really good reviews and decided to give it a try.

Yesterday I flushed my black tank out really well and following the directions, I added several gallons of warm water and the entire 32 oz. bottle of Unique Camping and Marine Tank Cleaner through the toilet, directly into the black tank. The directions said to wait at least 12 hours before flushing the tank again. I waited 20 hours.

After my 20 hour wait, I filled the remainder of the black tank with water and opened the valve to let the waste flush out. I have to say, I was a bit disappointed at first. I wasn’t seeing the amount of buildup moving through that I expected. After the first flush, I closed the tank again and filled it again. This time, when I opened the tank, I noticed a lot more debris flowing through. I went inside and looked down into the tank to see if the bottom looked clean. It was nearly clear so I flushed it out one more time and was completely satisfied with the results.

I’m impressed with the product and plan to use it every few months to keep the tank in good shape. I’m also planning on trying their holding tank treatment after I use the other brand I have on hand. I’d recommend this product for a stubborn clog or tank maintenance.


It’s been almost a month since I deep cleaned my black tank with Unique and I’m very happy with the results. Of course, there is always going to be an odor in the black tank but it’s at least 75% better since I cleaned it. I plan to repeat this process every six months to keep my tank from forming buildup.

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9 thoughts on “How to Get Rid of Black Tank Buildup”

  1. I have been using only dishwashing detergent in the black tank of my 2005 rig since I got it used in July of 2007. I put a squirt in the toilet about every third use. Still no visible build up when I look into the tank. I now have over 250,000 miles on the rig.

    1. juley.torkomian

      Hey Barney! I don’t generally get buildup in the black tank unless I’m pumping it out with the macerator. I may try your approach next time I’m parked in my daughter’s driveway for an extended period of time.

  2. You might want to remind your readers, when parked with sewer hookups, they should never leave the black valve open. It allows the water and liquid waste to constantly trickle out instead of helping dilute the solid waste. (RVers call that the “dreaded pile of doom”). That valve should only be opened to empty the partially filled tank, and closed again so the “slop” can accumulate. 🙂

    1. juley.torkomian

      Donna, You make a great point. I linked my long post about holding tanks near the top of the post for that very reason. It’s pretty in-depth.

  3. Pamela Grimes

    I still love Happy Camper that you had suggested to us first thing. I did read to add a cup of blue Dawn as it did clean the debris on our tank sensors.

    1. juley.torkomian

      Happy Camper is great stuff and I would still recommend it. My issue was a bit different though. Now that I love the cleaner, I want to try the treatment.
      Also, I have external tank sensors on the Airstream. I don’t miss those internal sensors at all. They never seemed to be accurate. Thanks for your comment!

  4. That’s a great recommendation. We all need that product!! My black tank is only 16 gals. I don’t put toilet paper in so that helps. Thanks Juley.

    1. juley.torkomian

      I’m really happy to know that layer on the bottom of my tank is finally gone. Funny things make RVers happy. 16 gallons must be challenging.

    2. Here is a FYI on camping toilet paper. When using toilet paper you can get camping toilet paper from any camping supply store. ( Camping World, etc.) However it is really expensive for what you get. The trick to finding the right toilet paper for campers is to take a quart jar full of water and drop a couple of sheets of toilet paper in it. Put the lid on it and shake it. If the toilet paper shreds it can be used for camping. We use Dollar Tree toilet paper. It is cheap and works great as apposed to expensive “camping” toilet paper.

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