A plywood box lined with mat or woven fiberglass and coated with resin is commonly used. Crates in a tank Either polyester or epoxy resin may be used. However, caution is needed with polyester resin. New polyester resin will leach styrene into the holding system. If it is a recirculating system, the styrene can accumulate to toxic levels.
Epoxy resin leaches fewer chemicals, but is four times more expensive than polyester.
An economical compromise is to fiberglass the tank with polyester resin and, after the polyester cures, coat it with one or two coats of epoxy resin. In either case, the tank system should be thoroughly flushed to ensure removal of all toxic leachates from the resin. To flush a tank, fill it with water and allow it to soak for 24 hours before draining it. This process should be repeated on a daily basis for a period of two weeks. The water should not have any resin taste or smell after flushing.