and concentric with the flow outlet to extend through the opposing side of the body so that the flow inlet 40 projects through a rear face of the body at the first portion thereof the flow inlet is internally threaded for receiving a standard plumbing fitting therein the threaded portion of the flow inlet 40 terminates at an internal shoulder where the flow passage increases in diameter for the remainder thereof towards the flow outlet the diameter is suitable for slidably receiving a pair of check valves in series through the open end of the flow outlet 38 for abutment against the internal shoulder 42 of the flow passage an internal annular groove 44 is formed adjacent the open end of the flow outlet for receiving a c shaped retainer clip 46 therein which selectively retains the pair of check valves 48 within the flow passage each of the check valves 48 is a self contained unit including a cylindrical housing a valve head a valve seat and biasing means for biasing the valve towards the closed position the check valve only permits flow in one direction therethrough the check valves are supported within the flow passage so that both are oriented to only allow flow from the flow inlet to the flow outlet through the flow passage in this configuration the two check valves 48 together form a back flow preventer or backflow prevention device in series with the flow passage a.