What fittings for fresh water tank?

[Xtremespeed]

I installed 2 white fresh water tanks but I'm worried about the fittings that attach to the tanks. I used pex tubing and shark bite fittings, but the fittings don't get very tight on the tanks no matter how much I turn them. I believe they are 3/8 pipe thread. Do I need special fittings here? Some kind of sealant?

[Shadow Catcher]

Our installation is PEX but the fittings into the tank are spin fittings which fuse themselves with the tank. There are fittings available to use with water tanks that are specialized. And yes the shark bite... fittings are not tight, they rely on an O ring for sealing. I made a number of modifications to our plumbing and I am waiting for good consistent warm weather to test for leaks but will do a pressure test using air from the compressor.

[Xtremespeed]

Thanks for the reply. I know the shark bite fittings are supposed to move, I was referring to where they are screwed into the tanks though. So I need to remove them and install special fittings. Will I have to get these from an rv supply store? What do I ask for? Spin fittings? My tanks have 3/8" female pipe fittings thermo welded to the tanks.

[Shadow Catcher]

If your tank already has fittings use them. The thermo welding is often accomplished by spinning, the friction of spinning the fitting against the tank is one way to accomplish that. This can also be accomplished using plastic welding which leaves a visible weld bead, this uses hot air and plastic welding rod. If you have an access in the top of the tank fittings that have an inside seal/gasket are usable and ports can be added to the top of the tank can be added if you do not have one. http://www.usplastic.com is a source for most everything plastic, they have it all.

[Dale M.]

If you are expecting a plastic fitting screwed into a plastic fitting to get really tight like a metal fitting.... Don't... Plastic fitting usually only need to be tight enough to seal.... If you think about it the male fitting will compress because its soft plastic (as opposed to steel or brass or copper) and the female plastic fitting will expand... The amount of "tight" you can get on a fitting is generally referenced the type of materials you are using...

A simple example if joining PVC pipe to steel pipe... IF you use a female plastic fitting and a male steel fitting, the plastic female fitting will fail because the steel pipe stretches it to beyond its burst point (tensile strength) ... But if you use plastic male into steel female it will last pretty much forever because the steel female will not expand past its tensile strength breaking point because the plastic male can not exert enough pressure to force steel pipe to break (again tensile strength) ... Learned this doing yard sprinkler system repairs....

Dale

[Xtremespeed]

Oops. Sounds like I should have used plastic fittings then. I hope I didn't mess up the threads on the tank. I used brass shark bite fittings. So I need to find some plastic fittIngs for pex tubing. Do I need any kind of sealant or Teflon tape, or just dry fit them? I take from your explanation that you don't put anything on them?

[Shadow Catcher]

I would use teflon tape and not worry about the fitting being plastic, brass will work fine and quite frankly you might not even need that. Just do a leak test, if it does not leak you are good to go

[Xtremespeed]

That's actually what I did. 1/2" male shark bite with brass reducer to 3/8" brass nipple with Teflon tape in to the 3/8" female threads on the tank. It just bothered me that I could easily move the fitting with my hand and I'm worried that it will leak. I don't think I have any way to connect my compressor to the tank to pressure test it. Obviously I'm no plumber. Lol!

[Dale M.]

Oops. Sounds like I should have used plastic fittings then. I hope I didn't mess up the threads on the tank. I used brass shark bite fittings. So I need to find some plastic fittIngs for pex tubing. Do I need any kind of sealant or Teflon tape, or just dry fit them? I take from your explanation that you don't put anything on them?

No not particularly..... Just screw brass fitting in enough that it does not leak.... Use Teflon tape if it suits you... IF it does not leak then there is no problem....

Dale

[Xtremespeed]

Thanks guys. Guess we'll just have to see this evening if it seals. The loose fittings just have me uneasy.

[Wobbly Wheels]

You can also use a polysulfide sealant on the fittings as long as it's food grade - Sikaflex 291 does it nicely and will prevent fittings from spinning. If you have a stub coming straight out of the tank, a metal fitting can vibrate enough to back itself out enough to leak through the threads - an elbow will prevent that.
Liquid teflon also has more 'grab' than tape does.

[Xtremespeed]

Got everything plumbed and none of the fittings leak. That would seem like good news, and it was until I noticed one of the tanks has a leak. I bought them a long time ago, so it looks like I'm going to have to buy another one.

[Martiangod]

Look for someone who does plastic welding, or get a plastic tank epoxy repair kit