Leaking domestic water tank

[grahamdouglass]

I replaced a degraded fibreglass water tank, that was 40 years old and leaking with a polypropylene tank. I asked for a topside inspection port. I was told it was water tight. It wasn’t even caulked to the tank. I tried Dow 732 silicone food grade caulking.
It’s tough to get a seal.

It only leaks when I fill the tank, the fill port is on deck and this tank is 3 feet below deck, below the floor boards in the lazaret. After I use a bit of water it no longer leaks.

If I can’t stop the leak I’m thinking of getting rid of the inspection port and patching the 8” hole caused by the removal of the inspection port. I have a separate air vent.

What is a good permanent bonding adhesive for polypropylene?
3m5200, epoxy ?

 

[RT Firefly]

Greetings,
Mr. g. What type of inspection port is there now? Is it similar to this or can it be replaced by this?

Deck Plate / Inspection Port : Attwood Marine

 

[Comodave]

You are not going to be able to get much if any caulk to stick to it for the long term. Will probably either have to weld it closed or install a clean out port similar to what is used on fuel tanks that through bolt with a gasket.

 

[grahamdouglass]

That’s what I’m thinking. Just patch it over. This is probably going to be a winter project. At that time I’ll remove the inspection port I have now and look at the various solutions.

 

[psneeld]

Use a neoprene or cork gasket.