3" EasyPro Bottom Drain w/Air Diffuser for Koi Ponds BDA has 1/2" barbed inlet fitting, recommended air flow through diffuser is .5 - 1.5 cfm For use with 3" schedule 40 PVC fittings and pipe Has dual rubber gaskets and six stainless screws for water tight penetration through liner 3" Bottom Drain with Air Diffuser