Thursday, June 1, 2023


RV holding tank crack


gary-736Dear Gary,
We bought a new Keystone fifth wheel toy hauler about a year-and-a-half ago. It went out of warranty after one year and now I have my grey water tank leaking badly when it is almost full. It is the tank for the shower and vanity.

I removed a section of panel under the unit to see if the tank could be repaired from underneath. I have access to the tank from under the unit and found a crack along the top edge of the tank and repaired it but it still leaks really bad when it is almost full. It appears to be coming from on top of the tank.

Can the tank be removed from under the unit by cutting the drain coming down into the tank and disconnecting the dump valve and the sensor wiring? It seems that if I remove a steel brace the tank rests on it should lower down underneath. There are four screws holding the brace the tank rests on. It doesn’t look as though the tank is screwed into the brace anywhere, so it seems that it should just lower down so I can see where the leak is and repair or replace the tank if necessary. It also seems as though the fifth wheel was built over the tanks and they could only be removed from under the unit. Any help would be appreciated before I do something that could be costly to reverse. —John C.

Dear John,
Yes, according the Standard for Recreation Vehicles, NFPA 1192, all holding tanks are to be installed in a manner that makes them accessible and removable in the field — even if you have to do a little digging to get to it.

Removing that steel support brace after disconnecting each of the drains entering the top of the tank as well as the vent (also required) should allow that gray tank to be removed. At the outlet of the tank, simply remove the waste valve by removing the four bolts at the termination assembly. I probably don’t need to remind you to perform these steps after the tank has been evacuated, flushed and drained again!

In some cases, access to the drain piping and vent pipe can be accomplished inside one of the interior cabinets. Simply cut through the ABS piping, near the floor, using a hacksaw. When reinstalling, simply glue an ABS coupling to rejoin the pieces.

Keep in mind, once you assess the crack, that the only permanent repair to a plastic holding tank is by plastic welding. Patch kits, although readily available in the aftermarket, should be considered a temporary repair only. Only by plastic welding can a tank be permanently repaired, so look for a shop or dealer with experience using a plastic welding machine.

If the crack is severe or located in an area under stress, it may be more practical to replace the tank. You’ll have to contact your selling dealer or Keystone in order to obtain the correct, exact replacement. In some cases, holding tank replacements are better left to the pro technicians, but in some cases an RV handyperson with adequate tools and an understanding of RV waste plumbing, repairs and replacements can be an alternate consideration.

Read more from Gary Bunzer at the See Gary’s videos about RV repair and maintenance.



0 0 votes
Article Rating
Subscribe to comments
Notify of

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Inline Feedbacks
View all comments
6 years ago

Try some of this new tape I see advertised on TV called Flex Tape.
Supposed to be waterproof.

6 years ago

Sometimes a leak on top that happens with a full tank is just the gasket for the vent pipe.

Sign up for the

RVtravel Newsletter

Sign up and receive 3 FREE RV Checklists: Set-Up, Take-Down and Packing List.