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How to Clear a Clogged RV Black Tank

  • 4 min read

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Article 6 of 8 in Series: RV Toilet Clogs

Read series from the beginning

Key Points:

  • Know for sure if you are dealing with a clogged tank before you start clearing it; misreading sensors can sometimes be confused with a clogged black tank.
  • Clearing a compacted tank is as easy as letting a tank full of water and a high-quality bacteria and enzyme tank cleaning product sit for several days and then dumping.
  • Additional treatments with water and tank cleaning products may be needed for stubborn clogs.

You may have heard horror stories of clogged black tanks (also known as a compacted tank) or have experienced one for yourself, so most campers know just how much of a headache it can be. If you’re already experiencing one, it can seem unsolvable, but it’s not. It’s actually one of the easiest clogs to clear. By following the steps described in this article, fixing a compacted tank is no biggie.

How to Clear a Compacted Tank


A compacted tank can be less of a headache to fix initially because the toilet pipe isn’t blocked by anything, so it’s easy to add water and product to your black tank. However, sometimes the compacted waste on the bottom of the tank can be extremely solid (especially if it has been allowed to dry while the RV was in storage), so though it may be easier to add water and cleaners to the tank, it can sometimes take significantly longer to break up the hardened waste.

Graphic representation of a compacted black tank

Misreading sensors can mimic the symptoms of a black tank, so know which issue you have by referring to our guide on What Kind of RV Toilet Clog do I Have?

  1. Close your black valve and fill the tank with as much water as possible.
  2. Pour one entire bottle of Clear-It into your tank through the toilet.
  3. Let the water and Clear-It sit in the tank(s) for at least 72 hours.

    Note: We always recommend at least 72 hours for Clear-It to work, but with compacted tanks, you may need to let it sit for longer than that because the waste is sometimes so solid that the solution needs more time to break it up.

  4. Open the black valve and dump the tank(s).
    • If nothing comes out, close the valve again and let Clear-It work for longer, possibly another 72 hours if you are able. If the blockage in the discharge line is very stubborn, you may need to use a PEX pipe to break up the waste so the rest can flow out.
    • If water starts coming out, dump the tank as normal.
  5. Thoroughly rinse your black tank.
  6. Close your black valve.
  7. Repeat this process again if you think there may still be some stubborn waste on the floor of the tank; as we said, you may need to let Clear-It work for longer than 72 hours to get every piece of waste to loosen.

    Important: When you are finished, be sure to close your black tank valve and keep it closed unless you are actively dumping a full tank. Refer to our guide on Why It's Crucial to Keep Your RV Black Water Valve Closed.

If you’ve followed the entire process above and still aren’t seeing results, please reach out to our customer support team. We are happy to help you get your clogged RV holding tanks back on track!

Misreading Sensors Falsely Indicating a Compacted Tank

Some people mistake misreading sensors for a clogged black water tank. Your sensors may tell you that the tank is full, but when you open the black valve to dump, nothing comes out of the tank. If you’re sure the tank is empty, then you probably just have debris caked on the sensors. The best way to confirm that the problem is misreading sensors is to add water to the tank through your toilet:

  • If nothing comes out of the tank when you open the black valve, then you have a compacted tank.
  • If you can dump it out of your discharge port but the sensor still shows full, then you’re probably just dealing with misreading sensors. Refer to our guide on How to Clean and Restore RV Holding Tank Sensors to return your sensors to proper working order.

If you follow the process for cleaning sensors and they are still misreading, they may simply be broken and need to be replaced.


Clearing a compacted tank is not a pleasant task, but now you have the steps you need to fix one if it ever develops again. Here’s a brief review of what we covered in this guide:

  • Make sure you know what kind of clog you have before you begin trying to clear it: compacted tanks and misreading sensors can share the same symptoms.
  • Fixing a compacted tank will require at least one bottle of Clear-It and possibly much longer than 72 hours for it to work.

You might have cleared the compacted waste on the bottom of the tank, but what do you do if you have a pyramid plug or a blocked RV toilet line? The previous two articles cover how to fix both of these clogs, but if you are concerned with preventing a compacted tank in the future, refer to our next article where we discuss all the habits you need to adopt in order to avoid clogs altogether going forward. 

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