Bought a used set of tailpipes they have a 3/8 male fitting on the bottom for a small hose? where would that go? or can it be pluged?

it returns to the back side of manifold

Thanks, But more questions? To the top of manifold or bottom where drain plug is? What is its purpose? Had many boats without this?

I was told it was to reduce stem pockets in the tails. There should two 3/8 nipples on the back side joined with rubber hose.

It connects to a fitting on the exhaust manifold with about a 4-6" piece of hose I don't think all the Gil manifolds had the other fitting though.
You can just cap/plug it if you don't have the matching fitting on your manifolds.

Thanks for all the advice.