Saturday, September 23, 2023


Ask Dave: How do I fix a crack on my RV’s gray water tank?

Dear Dave,
There’s a crack on top of my RV’s gray water tank. How do I fix it? —Buck, 2021 Puma Palomino

Dear Buck,
There are several products you can use to fix a crack on your RV’s gray water tank. Most tanks are made of polyethylene material and start off as small beads placed in a mold and heated while the mold spins in all directions. This melts the plastic and coats the inside of the mold, creating a seamless tank. This plastic is softer and more flexible than ABS plastic, which is used for shower stalls.

I would start by drilling a hole at each end of the crack on the gray water tank to keep it from going further. Then I’d clean the surface with rubbing alcohol.

Products to fix a crack on a gray water tank

There are several epoxies that mix two components and are applied to the crack. Or, another option is J-B Weld, which has a putty that claims to have a 600 psi strength, but I have not used it.

Another option that I have used is a plastic weld kit that melts plastic material that comes in sticks or rods and can be reinforced with a mesh patch if needed.

We’ve used this method before and it worked great. The kit we used had a small butane torch and a spin weld fitting that we needed to add a little more material.

Then there are always the “As Seen On TV” products. The one that stands out to me is Flex Tape. The commercial shows the salesmen slapping on some tape to the side of a plastic tank that is gushing out water, and later on a screen door on the bottom of a boat! I have not used it on tanks but have used it on the roof of RVs and trailers and it lasted for more than two years.

All of these products can be purchased on Amazon and are a relatively inexpensive fix for a crack in a gray water tank. The best one for your application depends on the accessibility to the crack, how large it is, and the level of work you are willing to do.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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Dave Solberg
Dave Solberg
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.


  1. Epoxy will not stick to polyethylene. Plastic welding would work but be very careful not to cause more damage. I would go with one of the tape options.

  2. How about Eternabond tape? I’ve used it on things, some of which were repaired years ago, and it’s still holding up. Never used on a water tank. Might be worth a try.

  3. The RV Geeks have stated that Flex Seal tape is NOT UV Stabilized and will fail over time when exposed to the sun.

  4. I have not used J-B Weld Plastic Weld but I have used regular J-B Weld on a deeply scored engine cylinder that lasted 17 years and was still running when I sold it. It’s great and “Tougher than nails” as the saying goes.


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