Just kind of sanded the outside of the hole (hull side) with a slight angle all the way around, instead of a squared off hole. Just a way to get more epoxy around the frp tube and bond it to more of the hull.
Same way you'd grind back a hull repair, but not so extreme.
I replaced the forward fish box drain on my buddies 23 seacraft with an FRP tube as well, but in his instance I did grind back the hull just as if I was doing a hull repair, and laid glass over the opening after I epoxied in the FRP tube. Then re-drilled it from the inside.
He likes to pound the crap out of the boat, so I thought a little more hull integrity couldnt hurt.
You just painted your hull didn't you? Might have to take the simpler approach to avoid having to repaint a section.