Floor Drain

A floor drain is a plumbing fixture set into a floor that channels water away from the surface and into the drain-waste-vent system. Floor drains are standard in basements, laundry rooms, utility rooms, mechanical rooms, garages, and commercial spaces. They serve as overflow protection (water heater discharge, washing machine overflow, pipe leak), direct drainage for equipment, and stormwater management in some configurations.

Anatomy of a floor drain

A typical floor drain consists of a cast-iron or PVC body with a removable strainer (the grate on top) and a built-in trap (a P-trap or drum trap set below floor level). The trap holds standing water — the same water-seal principle as any other plumbing trap — to block sewer gas from entering through the floor. Some floor drains include a sediment bucket (cleanout bucket) to catch debris before it reaches the trap.

The dry trap problem

Floor drains in infrequently used spaces (storage basements, mechanical rooms) are notorious sources of sewer gas odors. The trap water evaporates over months of non-use, removing the sewer gas barrier. Fixes: pour a gallon of water down the drain monthly; add a small amount of mineral oil to slow evaporation; or install a trap primer — an automatic device that injects a small amount of water whenever nearby supply valves are used.

Common issues

• Slow drain: debris accumulation in the sediment bucket or trap; clean annually
• Sewer odor: dry trap — see above
• Flooding during heavy rain: a sign the floor drain connects to a storm sewer that's backing up; a backwater valve upstream prevents sewage from entering through the floor drain
• Gurgling sounds: venting issue in the drain system; the floor drain trap is being siphoned

Maintenance

Remove the grate and clean the sediment bucket annually. Pour water in the drain monthly in seldom-used areas. A plumber can hydrojet a clogged floor drain line for $150–$400.