Drill holes in the flange of a 3/8 NPT threaded fitting to allow flox to grip it, then flox it into the side wall of each sump. Glass over the area with 2 BID, then carefully cut away the BID to uncover the hole. Cutting it with a razor blade is a better idea than using a Dremel, to avoid tank contamination from fiberglass dust.
These flanges will support the installation of a finger strainer in each sump (see Ingredients, Aircraft Spruce). Alternatively, you could drill and tap a piece of aluminum to do the same thing, but unless you need more 3/8 NPT holes tapped, two flanges are cheaper and faster than the tap.