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What Kind of RV Clog Do I Have?

  • 4 min read

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Article 2 of 8 in Series: RV Toilet Clogs

Read series from the beginning

Key Points:

  • RV toilet clogs are caused by three main issues: pyramid plugs, compacted holding tanks, or a blocked toilet line (misreading sensors can also cause you to believe you have a clog).
  • Diagnosing which type of toilet clog you are dealing with is crucial to solving your problem.

Using an actual toilet while camping is probably a big reason why you bought an RV in the first place, so dealing with a clog is never a fun experience. Before you can begin fixing a toilet clog in your RV, you need to be sure about which type of clog you are dealing with. Some RV toilet clogs have identical symptoms but different solutions. In this guide we’ll explain the different types of clogs you could have and how you can diagnose the clog that’s cramping your style.

What Type of RV Toilet Clog Could I Have?

There are three types of toilet clogs that you could be dealing with:

  1. Pyramid Plug – This is poop and toilet paper that accumulates into a pyramid shape right under your RV toilet line and has finally reached the top where it is now preventing anything from being added to the tank. A pyramid plug usually occurs when you have left your black tank valve open while on hook-ups because any liquid added to the tank immediately drains out of the open valve allowing accumulated waste to dry and build up. Always leave your black valve closed unless actively dumping a full tank. For more details on pyramid plugs, refer to our guide, What is a Pyramid Plug?

    Diagram of RV Pyramid Plug | Unique Camping + Marine
  2. Compacted Tank – A compacted tank just means that solid waste has accumulated in the bottom of your black tank, preventing waste from exiting the tank when the black valve is opened. This can occur if you are not using enough water in your tank, not using a high-quality, waste-digesting treatment, have a leaky discharge valve, or waste was left sitting in your tanks while in storage, which means the liquids eventually evaporate and the poop dries out, making it much harder to clean when you’re ready to use it again.

    Diagram of a Compacted RV Tank | Unique Camping + Marine
  3. Blocked Toilet Line – A blockage of toilet paper and solid waste can become trapped in the actual pipe that leads from the toilet bowl to the black tank. This problem mostly occurs in RVs where the toilet is not situated directly over the black water tank and the plumbing system therefore has turns and elbows where waste and TP can easily become congested. With systems like these where the toilet pipe does not empty vertically into the tank, it's best to use more water than you may think necessary when flushing. This type of clog shares the same symptom as a pyramid plug but has a slightly different fix, so be sure you know exactly which type of issue you are dealing with.

    Diagram of a Blocked RV Toilet Line | Unique Camping + Marine

Note: Misreading sensors that are caked with waste and toilet paper debris (black tanks) or grease and oils (gray tanks) can sometimes falsely indicate you have a clog, telling you the tank is full but nothing comes out when you open the black valve. It could be a compacted tank or it could just be an empty tank that has sensors falsely reading full. If all you have is misreading sensors, it is an easy fix. Refer to our guide on How to Clean and Restore RV Holding Tank Sensors.

Diagram of Misreading Sensor Probes | Unique Camping + Marine

In the next section, we will help you narrow down exactly what kind of clog you are dealing with so you can quickly take care of the issue.

Determine the Type of RV Toilet Clog

Knowing the type of clog you are dealing with is very important because there are different techniques you may need to use to free one clog as opposed to another type. We have provided a very easy litmus test below to help you determine what kind of issue you are experiencing, and the next article will show you how to fix it!

Add water to your black tank through your RV toilet bowl.

  1. If the water quickly collects in the toilet bowl when you push down the flush pedal, you have a blocked toilet line or a pyramid plug. 
    • If you have left your black tank valve open for any period of time, then you likely have a pyramid plug.
    • If you never leave your black tank valve open, you likely have a blockage in the line between your toilet and holding tank.
  2. If the added water easily flows into the black water tank, you have a compacted tank or misreading sensors.
    • If the water flows out of the tank when you open the black valve, you probably just have misreading sensors. Refer to our guide on How to Clean and Restore RV Holding Tank Sensors.
    • If nothing comes out of the tank when you open the black valve, you have a compacted tank.


Let’s briefly review what we covered in this guide:

  • Pyramid plugs form when you constantly leave your black valve open; all the liquid consistently flows out, and solid waste builds up right underneath the toilet line preventing anything from going into the black tank.
  • Compacted tanks develop when waste has accumulated on the bottom of the tank and prevents anything from flowing out of the discharge line.
  • Blocked toilet lines develop when toilet paper, solid waste, or a combination of those items clumps together inside the toilet pipe and blocks anything from being added to the black tank.
  • Misreading sensors can fool you into thinking there’s a clog when there is not; thoroughly clean the sensors if this is the problem.
  • Diagnose the clog you have before attempting to fix it; different clogs require slightly different steps to clear them.

Pyramid plugs are the most common type of clog campers will experience. In the next article, we will go into a little more detail about pyramid plugs and then show you how to fix them.

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