Help with gray tank knife valve connection

Question

I am having trouble with a gray water tank valve.  Last night water was running under the trailer.  I removed the black plastic belly cover, wet insulation and found that the knife valve connection was leaking between the valve and the tank.  The gray tank has a 1 1/2" outlet about an inch and a half long.  The knife valve was pushed into this outlet and glued with a butyl rubber and clamped with a hose clamp.  After cleaning everything up, I can not get the valve to stay in the tank outlet.  When I tighten the clamp the valve just pushes out.  This does not seem like a good way to attach the valve to the tank.  Is there a way to glue a short piece of ABS to the tank then glue the valve to the ABS.  What glue is used to glue the ABS to the tank?  I want to make sure that I can still service the valve so I am thinking that I do not want to use an epowy to glue the knife valve in the tank outlet which is why I would use a short piece of ABS first. Any help or ideas are appreciated as I am a long way from parts and need to be on the road the first of next week.

dr_quick · Answer

Most hardware stores that carry plastic plumbing pipe should have the cleaner and glue necessary to install the plastic pipe. Another possibility is, they make rubber connectors for plumbing pipe with a hose clamp at each end. Maybe you could find one that would fit your problem.

74vette · Answer

Is it possible to glue ABS to the poly gray tank with ABS cementor is there something better?

joe417 · Answer

ABS won't adhere to poly. The industry uses some type of adhesive but not sure what is is.

Of the two I currently have one has an outlet nipple heat welded to the tank and the other a rubber flange/grommet that is sealed with a flexible sealer and press fit into the opening.

The vent pipes on our 5thW are only pushed into the rubber flange as they want it to move with expansion. Obviously yours isn't just a vent so it needs to be sealed/clamped.

Both the poly nipples and the rubber grommets I have seen were sized exactly to the size of the ABS DWV pipe.

You mentioned gluing the valve to the pipe. Normally the valve is mounted with 4 screws and nuts in between two valve mounting flanges. Only the mounting flange is glued to the pipes.

You might post a picture. Some one on the forum has probably repaired one that's similar. Ask your local rv shop what they use.

74vette · Answer

Thanks Joe417
You are right, it is the flange that is pushed then glue into the tank. I have asked many RV repair people with no answer other than put it back with the flange glued with butyl into the tank. That is what I am going to do today as I need to get on the road. I have a hole cut in the belly plastic cardboard so I can moniter the fix. Will put the pan back without the insulation as I need to make sure it is correctly repaired first.

joe417 · Answer

There is no pressure except gravity on the tank, butyl should seal it provided you can get the clamp tight without pushing the valve out.

I found this on the HOBIE web site:

"It's hard to find glues to use on Polyethylene. Here's a list starter for things that work and those that don't.

Glues that work:

-- Scotch Weld DP 8010 by 3 M
-- Scotch Weld DP 8010 NS (same epoxy but with fillers)

Outstanding bonding. These glues are not the easiest to find, and not cheap. Price for small container is about $20; available through some R.S. Hughes, Graingers, Fastenal, and perhaps other industrial suppliers.

Tip: you can save the added expense of an applicator and dispenser if you're willing to push it out of the unequal cylinders and mix it. Five minute working time.

Glues that don't stick: (so far)

-- JB Weld
-- Super Glue epoxies (all -- verified w/ manufacturer)
-- Gorilla Glue (according to manufacturer -- didn't try it personally)
-- PVC glue, even w/ primer
"

Let us know if it works.

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Help with gray tank knife valve connection

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