Check the listing for details. 4" Bottom Pond Drain Kit + Bottom Diffuser w/ Fittings. Pond Liner Drain Part. Condition: New. Listed at 229.99 USD. Many pond builders have found that adding a bottom drain helps keep a pond cleaner. Fish waste and other muck that accumulates on a pond bottom can be easily removed by a bottom drain. Ponds that are over 2′ deep can become stagnant without a bottom drain. Details 4″ Heavy Duty Bottom Drain with Air Diffuser4″ EBD4A Bottom Drain Features: Heavy duty, roto-molded design offers superior strengthWelded FPT threaded inlet eliminates the need for rubber couplingThreaded center stand pipe securely attaches dome lid to baseSixteen stainless screws securely attach liner ring to base with water tight sealFor 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″ pipeEBD4A incorporates an air diffuser into the dome lid – incoming air is delivered up through the center stand pipe allowing air tubing to be installed under linerEBD4A tubing adapter is 1/2″, recommended air flow through diffuser is .5 – 1.5 cfm Also available in 2 and 3" - just ask us for the link to this one.