I know how unpleasant this is. If your washing machine standpipe smells even when the machine hasn’t been used, there’s usually a drainage problem that needs fixing.
Is this your problem?
The smell is coming directly from the standpipe
What to do
- If the smell is strongest right at the top of the standpipe, sewer gases are likely escaping.
- Check that the washing machine drain hose is pushed into the standpipe correctly. It should sit loosely and not create an airtight seal.
- If the standpipe has no trap (U-bend) or the trap has been removed during previous plumbing work, it will need replacing. A trap holds water that blocks sewer gases.
- This is usually safe to inspect yourself. If there is no trap fitted, a plumber should install one.
The smell appears after the washing machine has been unused for days
What to do
- The water inside the standpipe trap may have evaporated, especially in utility rooms or garages that are rarely used.
- Pour about one litre of clean water into the standpipe to refill the trap.
- Wait a few minutes and check if the smell disappears.
- If the smell returns within a day or two without using the machine, there may be another issue further down the drain.
The standpipe smells but drains perfectly
What to do
- A drain can smell even if water flows away normally.
- Soap residue, detergent, lint and biofilm can build up inside the standpipe and trap, creating unpleasant odours.
- Flush the standpipe with hot (not boiling) water, then use a drain cleaner that’s suitable for plastic waste pipes. Follow the product instructions carefully.
- If the smell remains after cleaning, the problem is likely inside the drainage system rather than the pipe itself.
The smell is worse in hot weather
What to do
- Warm temperatures make bacteria inside drains produce stronger odours.
- Clean the standpipe and trap thoroughly.
- Check that the utility room has good ventilation, especially if it’s enclosed.
- f the smell becomes much stronger during summer despite regular cleaning, have the drain inspected.
You can smell sewage elsewhere in the utility room
What to do
- If the smell isn’t limited to the standpipe, another waste pipe or trap may be causing the problem.
- Check nearby sinks, floor drains or utility basins.
- Run water into any unused drains to refill their traps.
- If several drains smell at the same time, the issue may involve the property’s drainage or vent pipe.
This is the point where a professional inspection is usually needed.
The standpipe gurgles as well as smelling
What to do
- Gurgling often means air is being pulled through the drainage system because of a partial blockage or poor venting.
- Look for slow-draining sinks or bubbling toilets elsewhere in the house.
- Avoid repeatedly using chemical drain cleaners if the blockage doesn’t clear.
- A plumber can check for blocked waste pipes or problems with the soil vent pipe.
The smell started after new plumbing work
What to do
If the washing machine was recently installed or the pipework was altered, the drain may not have been connected correctly.
Check that:
- The standpipe has a proper trap.
- The drain hose isn’t pushed too far down the pipe.
- There are no loose waste pipe joints.
If everything looks correct but the smell continues, ask the installer to inspect the work.
The smell keeps coming back despite cleaning
What to do
If you’ve cleaned the standpipe, refilled the trap and checked the hose position but the odour always returns, the problem is probably deeper in the drainage system.
Possible causes include:
| Possible cause | Safe DIY? | Professional needed? |
|---|---|---|
| Dirty standpipe or trap | Yes | Usually no |
| Dry trap | Yes | No |
| Partial drain blockage | Sometimes | Often |
| Blocked vent pipe | No | Yes |
| Faulty or missing trap | No | Yes |
| Drain or sewer fault | No | Yes |
When to call a professional
Arrange for a plumber if:
- The smell returns within a day or two after cleaning.
- You notice sewage smells in several rooms.
- The standpipe gurgles regularly.
- Water drains slowly or backs up.
- You suspect the trap is damaged or missing.
- There are signs of a blocked external drain.
Most persistent standpipe odours are caused by drainage faults rather than the washing machine itself. Fixing the underlying cause is the only long-term solution.