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Mark My Words: Fixing a leaking grey water tank

Q. We own a 1999 Tropi-Cal motorhome built by National RV. The company is now out of business. The gray water tank is leaking when it gets about two-thirds full. The tank was put on the chassis over the gas tank, and the floor and bathtub were then installed over the water tank.

Because of this installation, there is no way to get to the gray water tank to repair it. We dry-camp a lot and this leak is a real problem. Do you have any idea about how to fix it? Is there something we can put into the tank that would seal it from the inside or some way to get to it that we haven‘t considered? — Gary

A. That is a real problem, and I don’t know of anything that can be applied from (or to) the interior of the tank to fix a leak. Can you see the tank at all?

If any of the tank fittings are visible, eyeball them carefully for leaks. Most tank leaks are around a connector or sometimes around the tank sensor probes. You might get lucky and be able to identify and repair the leak without tearing everything up.

If you can’t see it at all, or the leak is not around an accessible fitting, then the only option is to get access to the tank. Is it possible to drop the fuel tank to get access to the gray tank? If not, there really is no choice but to tear up the floor to get to it. Bad design choices like that are all too common in RV construction.

Once you can get access to the tank, it is often fairly easy to fix. I have used eternabond tape, designed to patch roofs, with good results on several different tank materials. That stuff really sticks!

If your tank has a crack or split that is structural or caused by poor support of the tank, you may have to replace the entire tank rather than trying to patch it.

If you are faced with replacing a tank, be sure to contact the Tank Depot at

I don’t envy you your project! I recently had to replace my black tank on my Class C. It was poorly supported and developed a stress crack. All attempts to seal it failed, so I had to replace the whole tank and fix the support problem.

Thankfully, my tanks were exposed and accessible under the RV, so it was not that bad a job.

About Mark Nemeth

In 1997, Mark quit his aerospace engineering job and became a full-time RVer. For almost five years he traveled the country while maintaining his website, Mark’s Fulltime RV Adventure ( posting monthly travel logs. Mark now travels part-time and works as the RV Safety Education Director for Escapees RV Club providing technical training at Escapees Boot Camp seminars, as well as assisting in many other areas of the club. He is also technical advisor for Escapees magazine. Learn more about Escapees RV Club at

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