How to Use Oil to Seal a Floor Drain P-Trap

Updated: Feb. 15, 2023

A layer of oil keeps your floor drain sealed

FH05MAY_SEATRA_01-2Family Handyman
Keep water seal in your floor drains from drying out with a thin layer of cooking oil. It'll keep foul odors out of your house.

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Add cooking oil to floor drains

Add cooking oil

Fill the P-trap with water. Then pour a thin layer of cooking oil onto the water to keep the water from evaporating.

Under every drain in your house, there’s a trap that holds water and prevents sewer gas from flowing up into the air you breathe. But if you have a shower that’s been abandoned since the kids moved out or a floor drain that never gets used, the water in the trap can eventually evaporate. That lets in stinky—or even dangerous—sewer gases. The solution is a few ounces of cooking oil. Dump a bucket of water down the drain to refill the trap. Then add the oil. The floating oil forms a seal over the water and prevents evaporation—without raising your cholesterol.