"George Patterson" wrote in message news:QgHRg.1438$422.1197@trnddc03...
Head down to your local hardware store and pick up a few nylon machine screws
small enough to fit through the slots in your overflow. Drill your new black
plastic in locations that match the slots and run the screws through the plastic
and slots to hold the plastic panels in place.

Screws underwater might look too "technical" and not pretty.
Glue is more concealed.