My boat has a really old engine sea water intake. On the water side
it looks like shower drain...you know the kind...round with lots of tiny
holes. Inside is a threaded steel pipe (yep, old boat) with a hose barb.

Nigel Calder has told me all about installing a new one, but not
a word about removing the old one. So, what do I do? A slege
hammer from the inside to drive out the old thru-hull comes to mind,
but I bet that's not the correct way.

Regards...NormB