First, I had to seal the big hole with fiberglass epoxy. Bondo works well. Then I sealed the hole around the pipe with 3M  5500 sealant. Then I cut a neoprene gasket 1/8 inch thick to the size of the teak block and punched a hole in it for the pipe  to stick through. But I left the hole deliberately small so it would nipple around the pipe. Then I reinstalled the teak block. 55