A drain that smells bad has a specific cause. Most are simple to fix. Here is how to diagnose the smell based on where it's coming from.
Dry P-trap (seldom-used drain)
Every plumbing fixture has a P-trap - the curved pipe section that holds a small amount of water to block sewer gas. In Bloemfontein's dry winter months, guest bathroom drains, basin drains in spare rooms and floor waste drains that are rarely used can dry out. When the trap dries, sewer gas vents directly into the room. The fix is simple: run the tap for 30 seconds and the trap refills.
Blocked or partially blocked drain
A slow-draining basin or kitchen sink accumulates organic matter that decomposes and smells. The smell is strongest when you run water because air bubbles through the blockage. Clean the pop-up waste mechanism, remove any hair or food waste from the trap and pour boiling water with dish soap down the drain. If the smell persists, the blockage is deeper.
Failed vent pipe
Every drainage system needs a vent pipe to release gas from the sewer. If the vent is blocked by debris or bird nests, sewer gas has nowhere to go except back through the drains. This causes a persistent whole-house sewer smell that doesn't improve with cleaning. It needs a plumber to inspect and clear the roof vent.
Sewer line problem
If the smell is very strong, comes from multiple drains or is accompanied by slow drainage throughout the house, the issue may be in the sewer line rather than the trap or vent. Tree root infiltration, a cracked sewer pipe or a partial blockage close to the municipal connection are all possibilities. A CCTV drain inspection identifies the cause.
Frequently Asked Questions
Why does my kitchen drain smell even though it drains fine?
Grease buildup inside the pipe coats the walls and harbours bacteria that produce sulphur smells. The drain may be flowing fine but the walls of the pipe are fouled. A hot-water flush with enzyme cleaner or a professional jet clean resolves it.
Is drain smell from sewer gas dangerous?
In small amounts, sewer gas is just unpleasant. At high concentrations, hydrogen sulphide (a component of sewer gas) is toxic. Persistent strong sewer gas smell indoors needs investigation.