EasyPro - 4" Heavy Duty Bottom Drain with Air Diffuser Welded FPT threaded inlet eliminates the need for rubber coupling. EBD4A tubing adapter is 1/2", recommended air flow through diffuser is .5 - 1.5 cfm Threaded center stand pipe securely attaches dome lid to base Sixteen stainless screws securely attach liner ring to base with water tight seal Heavy duty, roto-molded design offers superior strength For use with 4" schedule 40 PVC fittings and pipe, use 4" male adapter (MA40) to connect to 4" pipe, use reducing male adapter (RMA4030) to connect to 3" pipe