Pentek 150235 20-BB 1-1/2" #20 Big Blue Filter Housing Large filter housing for high-flow and heavy sediment applications Reinforced polypropylene sump for strength and chemical resistance Use with a 20 x 4-1/2" filter cartridge (sold separately) Pressure relief button makes changing cartridges easier Initial pressure drop of 1 psi at a flow rate of 20 gpm