Bad threads on the water tank. Ideas?

[Raz]

The water tank in our Trillium sits in a molded well beneath the rear dinette. The drain pipe exits the drivers side of the well to a valve behind the rear tire. There is a 1/4" tee in this line that feeds the water pump. Very close quarters to say the least. The tank has always drained slow and never drains completely since the bottom of the tank is lower than the drain valve. Also there is always some wetness under the tank. I attributed this to sweating

[Raz]

The tank hole is 1/2" mpt, so I took the whole thing apart and replumbed with 1/2" tubing and raised the tank up so it will better drain. Unfortunately the threads on the hole are worn, apparently from the tank moving around, and will no longer seal tight. The wetness I thought was sweating must have been a slow leak.

There is no access to the inside of the tank and that hole is the only one that can be used. I am thinking of epoxying the fitting into the hole but thought I would see if any one has a better idea. Raz

[Donna D.]

Have you considered adding a deck plate to the top of the water tank? That would allow you to not only get all the water out, but thoroughly clean the inside as well.

http://www.fiberglassrv.com/forums/f...ank-49755.html

http://www.fiberglassrv.com/forums/f...ate-40482.html

[Thomas G.]

Originally Posted by Donna D.

Have you considered adding a deck plate to the top of the water tank? That would allow you to not only get all the water out, but thoroughly clean the inside as well.

http://www.fiberglassrv.com/forums/f...ank-49755.html

http://www.fiberglassrv.com/forums/f...ate-40482.html

It would also allow you to use a fitting with a nut on it on the inside to get a clamping seal as opposed to a thread seal.

I like your idea of raising the tank with foam insulation - I have the same issue.

[Raz]

The deck plate is the solution of last resort. Thanks

[Thomas G.]

Originally Posted by P. Raz

The deck plate is the solution of last resort. Thanks

I'd be tempted to use lots of Teflon pipe tape and put a pig tail in the line so the hose flexes instead of stressing the fitting in the tank when movement occurs.

[Raz]

Originally Posted by Thomas G.

I'd be tempted to use lots of Teflon pipe tape and put a pig tail in the line so the hose flexes instead of stressing the fitting in the tank when movement occurs.

I tried extra Teflon tape. The threads are too weak. The tank movement coupled with the stiff PEX tubing has really done a job on the threads. Right now I am thinking JB weld to make the fitting and the tank one and replace the PEX tubing with vinyl. Keep the ideas coming. Raz

[Thomas G.]

A two part epoxy like JB Weld might work. Would it help to put a stainless steel hose clamp around the outside of the protrusion of the tank? If you heated it and tightened the clamp at the same time you might be able to get it to get a better grip on the inner fitting.

[Darwin Maring]

Plumbers Goop?

[Thomas G.]

Originally Posted by Darwin Maring

Plumbers Goop?

Not a bad idea. This stuff is more flexible than epoxy when it has cured.

[Darwin Maring]

It appears to me that any tube of the goop will work. I think they are all the same formula and they just package it with different names just to sell the stuff. Shoe goop in the shoe department, plumbers, campers and so forth in the other departments. I always keep a tube around. It takes at least a day to set up and then cures for an even longer time and really holds. Because it's on your water supply I would be careful of toxic chemicals other adhesives may have.

[floyd]

What's the tank made of?
I.E. If it's PVC then you could simply glue in a PVC fitting after drilling out the threads. That fitting could have internal threads into which you could attach the drain line. If ABS then of course....

[Mouse]

What I did is choose a bigger threaded pipe and force it in the hole and having it cut new threads.

[artspe]

Raz,

I would try some GRIP (same as gasket cement used on cars). Than a stainless steel hose clamp as Tom had said. I would NOT try epoxy or pvc cement unless you know what the tank is made of (it might melt the tank if not compatable).

Art

[Bob Miller]

At your local autosupply there are items called "Self Tapping Drain Plugs" that are useful when your local $.50 oil change place cross threads your pan plug. These are designed to enlarge and rethread the hole at the same time. You might be able to use one of these to open and rethread the existing hole to the next thread size and use a new fitting.

[Raz]

Thanks all. Lots of good ideas. Not ready to cut new threads or go the Deck plate route yet. Floyd gets the prize for asking "What's the tank made of?" Turns out RV water tanks are made of polyethylene, similar to milk jug plastic. One of the reasons polyethylene is used for milk jugs is that it doesn't bond to other things. For that reason it can't be glued. Well almost. There are some products out that will stick to it. I am still researching. Raz

[john warren]

my guess is thats thermomolded plastic. epoxy might,,,or might not stick.
to properly repair it you would weld it. this is not very hard, and harbor freight sells a plastic welding tool pretty cheap.
another option is an rv dealer,,,i'm sure they have had this issue and may have the perfect adhesive for this repair.

[Andrew Gibbens]

Originally Posted by P. Raz

Turns out RV water tanks are made of polyethylene, similar to milk jug plastic. One of the reasons polyethylene is used for milk jugs is that it doesn't bond to other things.

Yes, gluing to polyethylene is a nightmare. Epoxy won't work on that - been there, tried that.

I've lost track of what the material you're trying to bond to it is, but if it's also plastic then I would go to a modelling (as in scale modelling) store as they have very good solvent glues that will work with most plastics. It's a very thin liquid so you apply it to the join between the assembled parts (yes, assembled) and capillary action draws it into the joint.

[Raz]

Here's what I have found out. There are several companies that make a adhesive that will stick to polyethylene. The only one I found that does not require special pretreatment or equipment is made by Loctite. Unfortunately it won't work in my application as it doesn't gap.

After reading everyones ideas, here is what I am doing. I tried Thomas' idea of adding a hose clamp around the outlet and it did indeed tighten things up. To fill the threads I am using a pipe joint compound paste (with teflon) suitable for plastics rather than Teflon tape. I let it cure over night. I am replacing all the pex pipe with vinyl for flexibity and will add some foam board on the sides of the tank to lessen its movement.

I suspect this is a short term fix. At some point in the future I will add an access hole (deck plate), drill out the fitting hole and add a brass nipple. Thanks again for all the ideas. Raz

[Tim Wood]

Raz, I probably missed something here along the way, but couldn't you find a new tank replacement and cut the old tank out ?