Kitchen and bath drains that get frequent use are usually full of water, but basement floor drains can dry out, allowing sewer gas in. To slow evaporation, fill traps with oil and water.
Top off the drain trap water level by adding a quart of water. Then pour in a couple of tablespoons of cooking oil.
The traps in floor drains—or for that matter, any drains that haven’t been used often—will eventually dry out. This may sound harmless enough, but a dry trap can cause a room to fill with potentially harmful sewer gas from the septic tank or the city sewer system. Phew! Eliminate this problem with a little fresh water topped with cooking oil (Photo 1). The oil floats on top of the water and seals it against evaporation. Your drain will hold water in the trap much longer.