Where does sewer smell come from
Every trap holds back sewer gases with a small amount of water. That water seal can disappear through evaporation, through siphoning when a large volume of water drains away quickly, or because another drain sucks the water seal out. The latter happens mainly when the soil stack vent is not working properly. The smell can also escape through a spot where the pipe itself is not sealed.
- A dry trap or floor drain that is rarely used
- A water seal siphoned out because of a blocked or missing vent
- An air admittance valve that no longer closes properly
- A loose or leaking joint behind the wall or under the floor
- Grease and soap build-up in the trap and waste pipe
- A loose cap on a rodding eye or inspection chamber
Vents and air admittance valves: the invisible link
A soil stack needs air to drain properly. That is why the pipe usually continues up through the roof, where it is open. When the toilet is flushed, the water displaces a large volume of air. Without proper venting, negative pressure builds up and traps on other floors are siphoned dry. You often hear this as a gurgling sound. So the smell is released in a different room from where you flushed.
During renovations, air admittance valves are sometimes fitted: small valves that let air in but no smell out. They work well, but the mechanism can get dirty or stick over time. The engineer checks whether the vent on the roof is clear and whether the valves still close properly. Where needed, a valve is replaced or the vent cleared. That way every water seal stays full and your home stays fresh.
What you can do yourself about drain smells
For a floor drain or shower that is rarely used, it helps to pour a bucket of water into it every week. That keeps the water seal full. Clean the trap under the basin and kitchen sink now and then by unscrewing it and rinsing it out. Do not pour frying fat or oil down the drain, as it sets and starts to hold odours. A clean trap is the first step towards a fresh kitchen.
If the sewer smell keeps coming back, even when all the traps are full and clean, the cause is usually deeper in the pipe or the vent. A targeted check is then the fastest route to a fresh home. Bosmans traces the source and puts it right, so you are not dealing with it again and again. Even with a smell that only appears in certain weather, such as strong wind or after a heavy downpour, the engineer knows where to look.
Sewer smell in apartments and commercial premises
In apartment buildings, several homes share a soil stack. A smell can therefore come from a connection in a neighbouring flat or from a blocked vent on the shared roof. Bosmans works in consultation with the owners' association or managing agent and maps the whole pipe. In restaurants the grease separator often plays a part too: a well-maintained grease separator and clean waste pipes keep the kitchen and terrace fresh.