Most older homes around Lancaster have a round floor drain somewhere in the basement, often near the furnace, water heater or laundry tub. It connects directly to the main building drain and the sewer. When it works, you never think about it. When it smells, you can’t think about anything else.
1. The trap has dried out (most common)
Every drain has a trap, a dip in the pipe that holds a little water and blocks sewer gas from coming back up. A floor drain that rarely gets water slowly loses that water to evaporation, especially in winter when the furnace dries the air. Once it’s dry, sewer gas rises straight into the basement.
The fix: pour a bucket of water down the drain, then a few tablespoons of mineral oil or cooking oil on top to slow evaporation. Repeat every month or two. If it keeps drying out, a plumber can install a trap primer or a trap seal insert.
2. A cleanout cap is loose or missing
Many basements have a cleanout plug on the main drain, a threaded cap on a pipe near the floor drain or at the base of the stack. If it’s loose, cracked or missing, sewer gas escapes. Tighten or replace it; a plumber can swap a corroded cast-iron plug for a new one.
3. The drain is partly clogged
Lint, sediment, soap and debris collect in the trap and the line beyond it, then start to rot. You may notice slow drainage when the washer empties or water appears around the drain. A plumber can clear the line with a machine auger from the cleanout. Our drain cleaning guide explains what’s involved.
4. The sewer lateral is cracked or blocked
If the smell comes with backups, gurgling toilets or several slow drains, the problem may be in the sewer line itself. Roots in old clay pipe, a sag that holds waste, or a crack under the basement floor can all push odor into the house. A camera inspection settles it. See sewer line repair.
5. A vent is blocked
Plumbing vents on the roof let gases out and let air in so drains flow and traps stay full. A vent blocked by leaves, a nest or ice can make drains pull water out of traps as they empty, leaving them dry. Gurgling sinks and slow drains alongside the smell suggest a vent problem.
| What you notice | Likely cause | First step |
|---|---|---|
| Smell only, drain rarely used | Dry trap | Pour water and a little oil in the drain |
| Smell near a pipe with a threaded cap | Loose or cracked cleanout plug | Tighten or replace the plug |
| Water pools when the washer drains | Partial clog | Have the line cleaned |
| Backups, gurgling, several slow drains | Sewer lateral problem | Camera inspection |
| Gurgling sinks plus the smell | Blocked vent | Have the roof vent checked |
If the smell is near the furnace, water heater or stove rather than the drain, treat it as a possible gas leak. Leave the house and call your gas utility or 911 from outside.
When it’s time to call a plumber
Try the bucket of water first. If the smell is back within a day or two, or if it never went away, something else is going on. Call a plumber if water backs up out of the floor drain, if you see sewage, if more than one drain is slow, or if the smell gets stronger when the washer drains or someone flushes upstairs. Those are signs of a blockage or damage further down the line rather than a dry trap. It also makes sense to have the drain looked at if your home has an old cast-iron or clay line and you’ve never had it inspected; a camera can spot cracks and roots long before they turn into a backup.
Most floor drain smells are a five-minute fix. If yours keeps coming back, a plumber in Lancaster can track down the cause.