I made plywood aquariums 40 years ago. At that time the plywood was srewed together using marine boat builder glue. The insides of my first one was painted with black asphalt paint. Later they were coated with epoxy resin.
The latest method is to glue a sheet of formica or arborite like is used for kitchen counters to a sheet of 3/4 plywood with contact cement. Cut your pieces to size and screw them together using silicone in the joints. A final bead of silicone inside makes for no leaks.
I hope this answers you with your questions.