Hydrotools 71604 Model 71604 Drain Plug and O-Ring Seal for Sand Filter Systems - This Drain Plug with O-Ring Seal is for use with Hydrotools Sand Filter Systems. Drain water from your HydroTools sand filter tank with the drain plug and seal set replacement for 16", 19", 22" and 24" tanks found on sand filter systems. These are genuine Hydrotools replacement parts.