Shawn: Yes, glueing a trimmed ABS pipe to the inside and trimming a hole to match the pipe's inside diameter would work -- hadn't thought of that approach, since I've mostly seen outlet pipes extending through the deck. Well, Last night I cut an elliptical hole to match the exterior of the pipe slanted downwards, so I think I'll consider your approach on my next boat.

I found that a Dremel tool really cuts fast when shaping the elliptical shape -- I can understand now why Pete Roszyk suggested using a metal template taped to the deck before enlarging the hole to its elliptical shape.

The pipe is mounted on a flat panel (Pygmy Arctic Tern), so filing and sanding the outlet pipe flush with the deck surface should be straigtforward, though I'll follow Pete's suggestion to put several layers of masking tape on the deck before I start filing.

Jim