Plastic water tank repair

[andytruck]

I have a poly 25 gallon fresh water tank. One of the threaded inlets is cracked, thanks to previous owner. I tried plastic welding, but no success (tank melts faster than the stick). I want to just glue the fitting into the tank so it does not drip, drip leak. Any suggestions on something to use that is not as permanent as the JB Weld I have on hand?
I tried plumbers putty heavily applied, but still leaks.
thanks

 

[rossvtaylor]

Without a pic, I'm guessing, but from your description I'm picturing a female threaded fitting that's split and when you thread the male pipe into it the fitting spreads and leaks. Is that about right? If so, can you use mechanical support (like a hoseclamp around the outside of the fitting) to keep if from spreading open?

 

[doug720]

Likely it's a "Bung" type molded fitting that sits just proud of the tank surface.

In plastic welding, and most welding, you need the correct size rod to the material thickness. If the rod is too thick, you melt the material you're trying to weld. If no other plastic rod, melt the rod first and work into plastic tank. Sometimes two heat sources and two people can make it work.

I have used soldering guns to repair plastic also.

You can check the West Marine catalogue for kits to install bungs into blank tanks - maybe a larger bung would allow cutting out the entire damaged area. Also contact RonCo Plastic Tanks and check this out - https://www.youtube.com/watch?v=crmnzfDZDPU

Hope these help

 

[javajoe79]

Can you cut out the bung and use a bulkhead fitting?

 

[andytruck]

Yes, is a female fitting that pokes out a little and has cracked.
I have tried welding with that stick on another fitting and just made a mess, tried melting the stick first but the fitting always sags and deforms before I can get it hot enough to stick. I am just not good enough at this to make it work. When it sags then the threads do not fit anymore.
Ideally I would just spin-weld a new one in, but it is insanely expensive for the tooling - cheaper to buy a whole new tank.
How would a bulk-head fitting work? all the ones I see you have to be able to get the part inside and part is bigger than the hole.
I may try using just silicone in the hole and hope no leaks. It is not under any pressure.

 

[doug720]

Silicone won't stick. Is this a drinking water tank? Be cautious of what you use to seal the tank. Some sealants can leach nasty things into your water...

There are kits to install bung fittings that bolt in. The top flange is 1 piece, the inner flange is 2 pieces. The inner and outer sandwich rubber seals to the tank.

 

[javajoe79]

Yeah a bulkhead would require you to be able to reach in to the hole from the inside