Why it matters to the pipes
Every drain in a house is protected by a trap, a U-bend that keeps a little pool of water in it and so keeps sewer gas from entering the room. Behind the traps, a network of vent pipes lets air move so that water drains smoothly without siphoning those traps dry. When a drain smells, one of these parts is usually out of order, or something is decaying inside the pipe itself. Sewer gas is unpleasant and, in quantity, unhealthy, so a persistent smell deserves attention rather than air freshener.
Have to hand
- A flashlight and a bucket
- Old towels and a pair of gloves
- The way to the main valve
Put the tools down if
- Water will not stop at the valve
- Sewage rises in a floor drain
- You smell gas near the heater
The steps, in order
Work through the possibilities from simplest to most involved.
- Refill seldom-used traps. A floor grate downstairs, the spare-room shower and the laundry sink all lose their water seal if unused for weeks. Pour a litre or two of water into each.
- Clean the overflow and stopper. Bathroom basins collect a slimy film inside the overflow channel and on pop-up stoppers. Remove the stopper and scrub both with hot soapy water and a small brush.
- Deal with biofilm. Kitchen and shower drains develop a coating of grease, soap and hair where bacteria thrive. A drain brush, hot water and an enzyme cleaner usually help.
- Check the dishwasher and disposer. Food trapped in a dishwasher filter or disposer chamber often smells like a drain problem.
- Note gurgling. If a fixture gurgles or its trap empties when another drains, the venting may be blocked or inadequate.
- Look for wet spots. A smell paired with damp drywall or a stain may mean a cracked pipe or loose joint.
Common missteps
- Masking the smell with fragrances, which hides the cause without fixing it.
- Pouring bleach repeatedly into drains. It does little against biofilm and can harm older pipes and rubber seals.
- Mixing chemical cleaners, which can release harmful fumes.
- Assuming a smelly floor drain is harmless. If refilling does not help, the trap or cleanout plug may be faulty.
When to ring for help
Call if the smell returns quickly after cleaning, comes with gurgling or slow drainage, appears in more than one room, or seems to come from inside a wall. These suggest a blocked vent stack, a failed seal under a toilet, a cracked pipe or a main line problem. Vent stacks can also be blocked by ice in a severe winter; our page on frozen pipe thawing touches on related cold-weather issues.
Drains that are noisy as well as smelly may share a cause, and our note on noisy pipes explains the connection. For help tracing a stubborn odour, call (365) 816-2905. We bring smoke-test equipment where needed to find leaks in the drain and vent system.