A sewer smell in the house almost always means gas from the drain system has found a way out: a dried-up trap, a blocked vent, a worn wax ring under the toilet or, further down the line, a problem with the main drain or the septic tank. At Wilfrid David in Chénéville, we check the simple causes first, then run a camera down the drain if the smell keeps coming back. If the smell is strong enough to cause a headache, open the windows and leave the room before looking for the source.
A dry trap, the most common cause
Every sink, shower and floor drain has a trap, the U-shaped bend under the fixture. It holds a small amount of water that acts as a seal and keeps sewer gas from coming back up into the room.
When a drain goes unused for several weeks, that water evaporates and the seal is gone. This is common in a cottage that sits empty part of the year, in a basement bathroom that rarely gets used, and in the floor drain next to the furnace.
The check is simple: run water for a few seconds in every drain that doesn't see much use. If the smell is gone within the hour, you have found the cause. If it returns quickly even though the traps are full, the water is not staying in place and the vent should be inspected.
The plumbing vent on the roof
The pipe that comes out through your roof lets air into the drain system. Without that air, water flowing down the pipes creates suction that can pull the water out of the traps as it passes. Typical signs are a gurgle in the bathroom sink when the toilet is flushed, or a drain that empties slowly and releases bubbles.
A bird's nest, leaves or winter ice can block a vent. For your safety, we recommend that you stay off the roof, especially when it is icy. Checking the vent is part of our work.
The toilet wax ring
Under every toilet, a wax ring seals the bowl to the drain. When it is crushed or cracked, the smell escapes at the base of the toilet, sometimes with no visible water at all. A toilet that shifts slightly when in use, or a stained or soft floor around the base, are common signs.
In that case, we replace the ring and check the condition of the floor while the toilet is off. It is best to find out early whether the subfloor has been absorbing water.
The main drain or the septic tank
In La Petite-Nation, many homes and cottages are served by a septic system. A smell that comes with slow drains throughout the house, or with water backing up at the lowest point (a floor drain or basement shower), points to the main drain or the tank: a full tank, a crushed pipe or roots in the line.
A strong smell outdoors near the leach field, with wet ground during dry weather, calls for a different diagnosis. We cover it in our article on the signs of a failing leach field.
In these situations, a camera inspection shows exactly where the blockage or break is before any digging begins.
Safety: sewer gas and propane
Sewer gas contains hydrogen sulfide, which has a rotten-egg smell. It can also dull your sense of smell, so no longer noticing the odour after a few minutes does not mean the gas has cleared.
If the smell is strong, or if anyone has a headache, nausea or dizziness, open the windows, leave the room and contact us. Avoid pouring a mix of cleaning products down the drain to cover the smell. It does not address the cause and can make the situation worse.
Propane also smells like rotten eggs; the odour is added on purpose so that leaks are noticed. If you have propane appliances and the smell seems to come from that direction, the Régie du bâtiment du Québec advises not to touch any switch, not to light anything, to shut off the supply if possible and to ventilate. If the smell persists, leave the house and call 911. If you are unsure which of the two it is, treat it as a propane leak.
When to call a professional
Contact us if the smell returns even with full traps, if you hear gurgling, if several drains are slow or if the toilet moves. We will locate the source and, if needed, carry out a camera inspection of the drain. If the septic system is involved, see our septic systems service as well. You can reach us at 819-428-3161.
Thinking of buying a property with a sewer smell in the basement? Read our article on camera inspections before you buy.
Filed under Camera inspection · Septic systems
