How to seal holding tank (plastic) fitting

[SVJOCO]

We have a plastic holding tank (PE) onboard where the discharge fitting mounts on the bottom (gravity emptying system).

It previously had a metal thruhull on it, but it was corroded badly and leaking so I removed it. All the other fittings are plastic.

I’m left with a hole (made by a hole-saw), where I need to mount a new fitting, preferably plastic, and I need to know the best way to seal it.

In the Todd fitting relocation kit instructions they say I can simply use silicone on it. Is that the best idea?

Preference for type of fitting? I have a 1 1/4” tru-design valve I would like to screw back on the fitting.

Thank you,

[billknny]

Silicone is generally the best when you are dealing with plastics. The polyurethane products (like 5200) do not stick well at all to most plastics.

You can also use a rubber gasket.

For a plastic tank, it is hard to go wrong with a PVC "bulkhead" fitting. Most of them will come with a suitable gasket.

[Bill O]

+1 for silicone.