Thetford tank flange leak

[sharp426]

I have a '87 Sovereign. I replaced the Thetford valves and black pipe. Both waste tanks are in good shape. I have the belly pan removed and the tanks supported. My problem is that I have a leak at both tanks flanges. I used plumber's putty between the tank flange and tank neck. When I had it all apart I didn't see anything other than plumber's putty between the flange and tank neck. When I reassemble I force the plumber's putty in the gap between flange and tank neck. As soon as the valve and pipe assembly are disturbed during belly pan install the flange-neck seal leaks. What do I do prevent this from leaking? Thanks for your help.

[ROBERT CROSS]

Make sure the flange is not cracked.
Ours was overtightened at install, was deformed and eventually started leaking.👎

Bob
🇺🇸

[Minno]

Plumbers putty won't work due to vibration. What is the tank made from? There is a rubber gasket that is made to go into the tank hole that the pipe slides into for a watertight fitting. Vintage Trailer Supply sells them. Called Rubber Tank Grommet.

Advice from hubby...


Kay

[sharp426]

I'm not sure what the tanks are made of. They appear to be the originals (1987). It's white (translucent). I'll look into the grommets. Thanks.
When I disassembled I didn't see grommets, only saw a pliable white putty like substance. I agree with the idea that vibration, and reassembly, will cause the parts to change position slightly and cause a leak.

[CRH]

I did my valves about 5 years ago. I don't recall any large rubber grommets.

[Ultraclassic]

I cleaned up black tank valve and wet sanded the gate and lubed the sealing surface, seems to work good now, had some "seeds" stuck in the gate path

[sharp426]

Ultraclassic, How are your tank flanges sealed to the tank? Mine only had a white pliable (non hardening) putty sealing between the tank neck and the flange.

[sharp426]

I believe my tank is made of polyethylene. The pipe nipple is part of the tank, the mounting flange for the Thetford valve is not glued or permanently attached to the waste tank pipe nipple. When I took the system apart it only had a pliable putty like substance in the flange groove that is forced up against the waste tank pipe. I don't know where to get the putty or if I can use an o-ring along with the putty.

[GCinSC2]

Sharp426,

I replaced one flange last week on my 2007. Valterra components. But the flange was a slip fit, external band clamp. But the sealant was a mystery.

Cleaned up tank fitting, new flange and my dealers tech said use butyl rubber sealant adhesive.

Used it, let it cure for day and half then filled with water. Did not leak.

In my area not found at usual sources but found at RV shop as skylight sealant, it was butyl.

Gary

[A W Warn]

Originally Posted by sharp426

I believe my tank is made of polyethylene. The pipe nipple is part of the tank, the mounting flange for the Thetford valve is not glued or permanently attached to the waste tank pipe nipple. When I took the system apart it only had a pliable putty like substance in the flange groove that is forced up against the waste tank pipe. I don't know where to get the putty or if I can use an o-ring along with the putty.

I replaced a dump valve on a 1987 I owned about 25 years ago. I remember that it did not have a tank adapter, the valve slipped into a nipple/coupler that was built into the tank.
I used caulk, not plumbers putty. I am fairly certain that it was the parts guys at Out of Doors Mart told me to use polyurethane sealant.
https://odmrv.com/catalog/index.php?...mjfl31b11dv5d7

ps:
A couple years ago I replace the dump valves in my 1999. I used Lexel caulk on the tank adapter/tank coupler joint, because it will seal to a wet surface. Since I was living in the trailer away from home while doing the repair I didn't have time to dry it.

[A W Warn]

Originally Posted by GCinSC2

Sharp426,

I replaced one flange last week on my 2007. Valterra components. But the flange was a slip fit, external band clamp. But the sealant was a mystery.

Cleaned up tank fitting, new flange and my dealers tech said use butyl rubber sealant adhesive.

Used it, let it cure for day and half then filled with water. Did not leak.

In my area not found at usual sources but found at RV shop as skylight sealant, it was butyl.

Gary

Do you have a thread about your repair? It would be beneficial to others who want to do the same, to have a material list and a few photos.
When I replaced the valves in my 99, I could not find Valterra components that would work.

[GCinSC2]

A W Warn,

No I didn't make a thread.

Lessons learned from ONE R&R of both valves on a 2007 30'.

Make a layout of the valves, pipes etc on your access panel on the bottom of the pan as a guide. Your cables for tank sensors are in this area too.
Suggest use power snips. I did it with aviation snips, doable but not really fun.
Deburr edges of pan and cover edge with masking tape. Bandaid count was zero.
I used a hole saw at corners for snip access. Also I cut a length of PVC pipe that slid over the hole saw and made a depth stop to prevent saw from punching thru and damaging stuff. Same technique but used copper 1/4" tubing for drill limiter to install new cover.
Removing old flange from tank, twist a bit, pull a bit, rock a bit and repeat. That broke the bond but nothing else.
Applied butyl in the tank and flange, slid in with some twisting.
My AS tech guru also said to let it set for about 1 hr then tighten band clamp.
Fill each tank with water for leak testing prior to celebrating.

If you do your pre planning and get the layout of the valves you could do a more surgical approach and not make a full size access panel, I tried and could get to valves and R&R but a flange crack made it prudent to make full size access pan.

At my house I have a flat to sloped driveway. I backed AS rear tires right to the transition to slope and this made a good overhang and gave me decent access to the job.

The butyl was the oh yes we USED to carry it but no more. After it cured I felt the butyl and it was non hardening chewing gum like feel.

My valves were still OK but found inner seal on grey was degrading. this was a pre-failure R&R on my terms.

Gary

[pliddell]

I've just attempted to solve the same problem. I have not tested it yet but I used Dicor cap sealant 351CST-1. Be sure to scrape off all the old sealant and have a flat surface where the neck of the tank flange seats. I applied it liberally over the entire inserted surface, inserted with half twist and then reassembled the remaining piping. The clamp was tightened after the plumbing was replaced (done right away).
AGAIN, untested. I found the old type of clamp at the auto shop and it is called a T-Bolt Clamp. What they had was a 3" which will not work but if I ever have to get under this thing again I'll order the next size up to use. These are nice because they are wider than the new ones. The disadvantage might be accessibility since they tighten with wrench rather than a flathead.