Seems the waterline in your sump leaves plenty of volume to catch water in case of a power outage. Leave your return lines as high as possible in the tank; in case the power goes out, the air will break siphon and you won’t have to deal with a wet floor. You can get a sheet of plastic from TAP Plastics, HD or Lowes as Mark suggests;
Iquid Nails should do a good bonding on the drywall.
Iquid Nails should do a good bonding on the drywall.