RV Quickie Flush with Back Flow Preventer - The Camco RV Quickie Flush with Back Flow Preventer helps to thoroughly flush the RV holding tank without bringing a hose through the window. This permanently installed built-in backflow preventer keeps sewage from contaminating the water line. Simply hook your garden hose on to the connection outside the RV (which has been installed with hose to the sewer tank) to run fresh waer through the tank and dump hose so that it flushes out the tank and hose completely. Flush for 2 minutes or until water from discharge hose runs clear. 1 per package.