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Unclogging A Plugged RV Black Tank

August 06, 2020

Learn how to unclog a plugged holding tank in minutes. Learn more here!

RVers of every experience level will sooner or later hear of or experience the dreaded “holding tank clog,” a seemingly undefeatable beast! But we’re here to tell you, holding tank clogs don’t have to be a scary ordeal. By following the right steps, you can beat them! More than that, if you put the proper care habits into place, you can prevent them from ever happening again!

In this article, we’ll be discussing the compacted tank. In its simplest form, this is a very accurate description! A compacted tank occurs when your entire black water holding tank (or at least a significant portion of it!) becomes clogged with compacted waste (in essence, a big block of often dried out, solid poop and toilet paper!). This can occur for a couple reasons:

  1. Waste has been allowed to accumulate inside your tank and solidify, preventing you from dumping. There are several reasons this can happen: 1) you aren’t using a high-quality holding tank treatment, 2) you aren’t following the proper treatment practices (which we outline in The Unique Method!), or 3) you didn’t dump your tank before storing your RV and the waste has dried out on the bottom of your tank. 
  2. Solid waste and/or toilet paper became lodged in your discharge pipe (the line between the black tank and the black tank valve) and caused a blockage. Again, this is normally caused when you don’t use a high-quality holding tank treatment—like RV Digest-It—or you haven’t been implementing the proper care habits.

We’ll examine these reasons more fully later on, but first you must determine if you indeed have a compacted tank as opposed to the other two types of holding tank clog. 

How to Diagnose an RV Holding Tank Clog

Lucky for you, a clogged/compacted holding tank is probably the easiest type of clog to diagnose. Simply follow these steps to determine if you have a compacted tank.

  • Step #1: Open your black tank valve. If nothing comes out of your tank, you may have a clogged/compacted tank—but it could also be a pyramid plug. Be sure to close your black tank valve before you move on!
  • Step #2: Flush your RV toilet. If water flushes down your toilet and into your black tank, then you most likely don’t have a pyramid plug. You might, however, have a compacted tank.
  • Step #3: Open your black tank valve one more time. Watch if the water you just flushed down your toilet comes out of your tank. If no water comes out, then you have a clogged/compacted tank! If water DOES come out, this means you probably have no clog at all and your sensors are probably just malfunctioning and reading “full”. We have a very extensive and helpful guide for cleaning and restoring your tank sensors if this ends up being your situation.

Now that you know whether or not you have a clogged/compacted holding tank, we can move on to how to fix it! 

After you've gone through this diagnoses, does it seem like this ISN'T your problem? Read here to diagnose if you have one of the other common tank clogs and learn how to solve it!

How to Unclog an RV Holding Tank

A clogged/compacted tank is relatively easy to fix because you can easily add water and Unique Tank Cleaner to your holding tank through your RV toilet! Indeed, adding water is the ultimate goal here. Water will allow Tank Cleaner to break up the clog. 

Follow these steps to unclog your RV holding tank:

  • Step #1: Close your black tank valve and add as much water to your tank as possible. 
  • Step #2: Pour 1 bottle of Unique Tank Cleaner into your tank through your toilet. Allow Tank Cleaner to work for at least 72 hours, but keep in mind that you might have to let the product work for longer. A compacted tank often takes more time to break up since the compacted waste is so solid. 
  • Step #3: Open your black tank valve and empty your tank. 
  • Step #4: Run your tank rinser or flusher for 20-30 minutes. 
  • Step #5: Close your black tank valve. 
  • Step #6 (optional): Repeat steps 1-2 if necessary. As we said, a compacted tank is often made up of extremely solid waste that has been allowed to dry out/become very dense. Because of this, you may have to give Unique Tank Cleaner extra time to work and/or add more product to your tank. Tip: if you’re having lots of issues getting your tank to empty out, one thing you can do is (very very gently!) tap your discharge pipe with a soft object like a shoe or rubber mallet. This can help to break up and dislodge any residual waste stuck in your discharge pipe. You can also use a length of PEX pipe to help break up waste stuck in your discharge line. 

How to Prevent A Clogged/Compacted RV Holding Tank

Like we covered earlier, a clogged/compacted RV holding tank occurs when solid waste builds up on the bottom of your tank or clogs your discharge line, preventing you from dumping your tank. There are several ways to prevent this from happening in the first place.

  • Make sure you’re following The Unique Method’s most important rules: 1) keep your black tank valve closed unless you’re dumping your tank and 2) use plenty of water in your tank. More water = less likelihood that you’ll experience clogs!
  • Use a high-quality, bacteria-based holding tank treatment—like RV Digest-It. A quality treatment product will help break down the waste in your tank, preventing it from solidifying. 
  • Never store your RV without first dumping and rinsing your black tank! Storing your RV with waste still in the black water holding tank is a surefire way to develop a compacted tank. After you put your RV in storage, all the water will evaporate from your black tank, leaving behind a dried-out block of solid waste that is difficult to remove! This is why you might need to give Unique Tank Cleaner extra time to work on a compacted tank. The waste that makes up this clog is often so dense that it takes even bacteria a significant amount of time and effort to break it up!
  • Follow The Unique Method, which will outline for you all the proper care habits that will help to keep your RV clog-and-odor free in the future!


Clogged or compacted RV holding tanks can certainly seem unbeatable at times, but as we’ve shown, you can defeat them if you follow the right steps and prevent them if you implement the right procedures! 

As you know, there are other types of RV holding tank clogs, namely, pyramid plugs and blocked lines. If you are interested in learning more about these clogs, how to fix them, and how to prevent them, please check out our thorough article, Unclogging An RV Toilet!

We hope this article has been helpful! If you should have any further questions about this topic that are not answered in this article, we’d love to hear from you! You can reach us at  support@uniquemm.com.

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