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RV Holding Tank Shapes - Could Yours Cause Waste Build Up?

  • 4 min read


  1. Knowing the shape, design, and placement of your RV holding tank is crucial in preventing backups, pyramid plugs, and clogs.
  2. 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, and (2) use a high-quality, waste-digesting RV holding tank treatment. 

Believe it or not, the actual shape of your RV holding tank can be a big reason why you struggle with wastewater holding 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 issues in the future. In this guide, we’ll cover some of the biggest structural features in regard to 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

Why is your holding tanks’ shape important? It’s important because certain holding tank design shapes are more prone to clogs and are harder to clean than others. Believe it or not, nearly all RV holding tanks use only 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.

The majority of tanks have a flat bottom. This flat bottom can actually cause clogging issues. For instance, if you leave your black water holding tank valve open (which is generally not a great practice), the water and urine are able to flow out of the tank with relative ease, while the toilet paper and solid waste get stuck to the bottom of the flat tank surface, unable to flow out and into the sewer. Over time, this can become an actual pyramid of poop and toilet paper!

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.

The solution to this shape problem is fairly simple. Following The Unique Method and flushing your tank very thoroughly on a regular basis will help prevent this old waste from building up over time. Remember though, just flushing your tank for a couple minutes until "the water comes out clear" doesn't mean that you are cleaning up that old waste that has hardened in the corners of your RV holding tank! To rinse out this stubborn waste, it often takes flushing multiple times before you get a second round 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.

Guide Continued Below

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Mind The Lip

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!


The reality of holding tank issues is that they’re designs are all unique. Containing waste while on the move is a messy subject and can cause huge headaches for RVers. However, if you stay on top of things by 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! We’re always happy to help! Happy camping!

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From misreading sensors, preventing clogs, or eliminating odors, we've got you covered no matter how you camp! All our best holding tank tips and trick information plus more can be found conveniently in one place when you download our FREE Unique Method Field Guide PDF. Achieve holding tank bliss today!

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