Which sealant for polyethylene holding tank

[crazyoldboatguy]

I'll never use silicon sealer on a boat again. You can't get all the stuff off if you have to. It leaves a residue that is a royal pain in the ass to deal with.

It will probably be fine in your application.

As for myself - I used 5200 when I bedded a thru hull into a polyethylene tank I installed as my holding tank. I did that 10 years ago. Not a single leak. Since it isn't likely to bond to the tank - if I have to remove the fitting it isn't likely to be a problem.