Flood-Guard™ operates like a check valve to seal off water back-up caused by overloaded sewers. Water flows normally through the drain until the sewer begins to back up. Then the Flood-Guard™ float rises to seal off the drain opening until the water recedes. A screwdriver and a couple of minutes are all you need to install a Flood-Guard™. Once in place, it can prevent property damage and a very messy clean-up job. For extreme, extended pressure (for instance, where home-made seals have popped out of the line,) we recommend our standpipe models. The 4" Standpipe Flood-Guard™ is threaded to receive 1-1/2" IPS pipe. On the 3" model, the pipe is slipped through the rubber gasket before the screws are fully tightened. Gaskets are made of molded rubber, and all metal parts are plated or stainless steel.