Edge for bubbler top

[Picturebel]

Hi everyone. We have just built a new pool and had 3 by bubblers installed on our wide step. Basically the conduit finishes flush with the step but of course there is a rough edge. I am needing something to finish it. I'm thinking a plastic that we can glue snug inside with a small lip on it to cover the top edge. One company has said it's too small for their machine to hold.
Any ideas??? Thanks!