Stop sewer gases from escaping through your floor drain if the P-trap dries out. Similar to a check valve, they allow liquid to drain but won’t let gases back up. They’re especially useful in infrequently used drains. To install, remove the strainer from your drain and place these seals in the opening. They have fins that grip the inside of the drain and a top ring to keep them in place. After putting the strainer back, pour water through the drain to fill the P-trap.