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RV Holding Tank Shapes - Could Your's Cause Waste Build Up?

March 25, 2020

What is the shape of my rv boat camper trailer fifth wheel black gray water holding tanks and how does it lead to clogs pyramid plugs poop pyramids blockages blocks backups back-ups leaving your black tank valve open


  1. Since RV holding tanks use gravity to drain and most tanks have flat bottoms, you may experience issues with pyramid plugs or residual waste buildup if you (1) leave your black tank valve open or (2) do not properly rinse out your tank for 20 – 30 minutes. 
  2. While most RVs have toilets positioned directly over the holding tank, others have long and winding pipes leading from the toilet to the holding tank. These long pipes can easily clog, but using plenty of water in your toilet bowl (1) before and after you use the bathroom and (2) when you flush can help you avoid backups in the plumbing.
  3. To help mitigate problems that can occur because of oddly shaped RV holding tanks, we recommend that you (1) rinse your tank for longer periods, (2) use a high-quality, waste-digesting RV holding tank treatment, and (3) fill your RV toilet with water before and after each use.

Believe it or not, the actual shape of your RV holding tank can be a big reason why you struggle with waste tank clogs! The construction and design of your holding tank, as well as how it's mounted to your RV, have a surprisingly big impact on how susceptible you are to getting pyramid plugs and clogs in your tanks. Understanding the shape of your holding tank can help you avoid these messy mistakes. In this article, we’ll cover some of the biggest structural problems with your RV's holding tanks, as well as some treatment techniques and advice to keep your RV tank clog-and-hassle free!

Holding Tank Shape

To get started, let's go over some holding-tank-shape problems of which you should be aware. First, why is your holding tanks’ shape important? It’s important because certain shapes are more prone to clog and harder to clean than others.

Quick fact: Nearly all RV holding tanks use gravity to drain. In other words, there is nothing pushing the water out of your tank; it's just naturally flowing out. So the geometry of a holding tank can cause issues if water isn't easily able to flow out of the tank.

For example, one issue we all-too-frequently help customers solve is "pyramid plugs" (i.e., literally poop pyramids!). These plugs are a direct result of two things:

  1. Leaving your black tank valve open
  2. The flat bottom of your tank

When you leave your black valve open, the water and urine are able to flow out of the tank with relative ease, while the toilet paper and solid waste fall to the bottom of the flat tank surface. Over time, this can become an actual pyramid of poop and toilet paper! (Gross, we know!)

But here’s the great news: you can prevent these plugs by following The Unique Method! The Unique Method is a proven holding tank treatment process we have developed over the years from thousands of conversations with RVers around the country. It is an easy process to follow and will virtually eliminate all problems with odors, clogs, and pyramid plugs! Read more about The Unique Method here.

Another problem we hear frequently has to do with old, dried-up waste collecting in RV holding tanks—even when you are treating your tank with a high-quality waste digester and flushing your tanks! The reason for this is that most holding tanks are not installed perfectly level, nor do most RVs get parked perfectly level, so it's only a matter of time before waste starts to build up in the nooks and crannies (the corners) of your tank, because it cannot flow out with gravity.

Herein lies another reason why it's so important that you follow The Unique Method and flush your tank very thoroughly on a regular basis. Just flushing your tank for a couple minutes until "the water comes out clear" doesn't mean that you are cleaning up that crusty, old waste that has hardened in the corners of your RV holding tank! To rinse out this waste, it often takes flushing for a significantly longer time—20 to 30 minutes—before you get a second whoosh of black tank waste leaving your holding tank. The reason for this is that gravity alone cannot empty the liquid and solid waste from un-level tanks. Over time, there is bound to be residue.

Build-up can be even worse if the holding tank doesn't drain out of the bottom of the tank. On many tanks, the drain is mounted on the side of the tank. Because of this, there will often be a lip that retains a layer of waste on your tank's floor, making it hard to drain all of the waste. This is another reason why you should regularly flush your tanks very thoroughly!

If you're having an issue with clogs and want specific help unclogging your RV toilet, check out our comprehensive article on Unclogging An RV Toilet by touching or clicking here.

Holding Tank Plumbing

Now that we’ve talked about your RV holding tank, let's talk a bit about plumbing.

The plumbing in many RV bathrooms is configured with the toilet directly above the holding tank, so it is a straight drop to the tank. However, there are also many RV's where the toilet is not directly above the tank, so long and winding pipes may be required to deliver your toilet waste to the holding tank. As you can imagine, it’s fairly easy to get paper and feces clogged in these lines before they even reach the tank!

An RV toilet that drops straight into the holding tank is far less prone to getting backups in the line, but it can still happen. 

Avoiding back-ups in the plumbing before the holding tank is simple: Water!

  1. Always fill your toilet bowl with water before and after you go to the bathroom.
  2. Hold your toilet flush pedal down for 10 seconds each time you flush.

If you fail to do these two things, don’t be surprised if toilet paper and waste get stuck in your pipes! Also, using too much toilet paper can lead to clogs and back-ups in the line, so be careful to not use too much.

Besides clogs, having extra plumbing between your RV toilet and your holding tank also means that you are more susceptible to leaks in some form or another—especially if your plumbing isn't well insulated and temperatures get below freezing. We recommend periodically doing an audit of your wastewater systems to make sure everything is in good shape.

The simple fact is that problems can occur whether your RV is brand new or used, and each manufacturer does things a little differently, so it is up to you to follow good holding tank habits and thus avoid costly and disgusting repairs. Remember, we are always here to help you along the way!

Our Recommendations

There are a lot of differences from one RV to another—especially when it comes to wastewater systems—but there are a few key things you can do to help keep some of the possible issues at bay regardless of the brand or model of RV you have:

  1. Rinse your tank for longer periods. We suggest 20-30 minutes of running water to make sure all of the nooks and crannies in your holding tank are clean.
  2. Use a high-quality, waste-digesting RV holding tank treatment like RV Digest-It. By using a waste-digesting treatment, you’ll help to break down solid waste in your tank and prevent buildups and clogs.
  3. Fill your RV toilet with water before and after each use. This will help to keep plumbing from getting backed up or compacted. 


The reality of holding tank issues is that they are all unique. Containing waste while on the move is a messy subject and can cause huge headaches for RVers. However, if you’re diligent with properly treating your water systems, you will help mitigate these potential problems!

Remember, we are always here as a resource for you. If you are ever dealing with a waste issue in your RV, we are here to help! Please contact us! They will work to get you back on the road!

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