Its one of the best sealants available but if you use too much it will break away and cause issues. I have used ultra blue on sump plugs in the past but you have to make sure that you clean out the threads on the box each oil change otherwise your just going to push any loose sealant into the box.

So what do use these days on sump plugs (if any)

If you have a new copper washer and good threads it should seal. The copper washer does the sealing but the threads keep the plug centralized so the mating surfaces are square when tightened. A bit of sealant on the copper washer and mating surfaces will help if needed. Check the mating surface on the box for burrs, scratches or wear.

I use Stag jointing compound on almost everything.
Seems to do a good job on anything.

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