A sewage or drain smell is almost always trapped organic debris — food particles decomposing somewhere in the filter, sump, or drain hose — rather than a fault with the machine itself. Unlike a washing machine, which more often develops a musty biofilm smell, a dishwasher’s smell profile leans toward this trapped-food pattern because of what actually goes through it on every cycle.
Why dishwashers develop this smell
Every cycle carries food particles through the filter and drain system, and while the filter catches most of it, some residue inevitably remains behind in the filter housing, the sump beneath it, and along the drain hose. Left long enough between cleans, this residue decomposes — which is exactly what produces a sewage-like smell, even though nothing about the machine has actually malfunctioned.
Common causes
| Cause | How likely | Typical sign |
|---|---|---|
| Food debris built up in the filter | Very common | Visible residue when the filter is removed |
| Grease and food residue in the sump | Common | Smell persists even after cleaning the visible filter |
| Drain hose harbouring residue | Common | Gradual smell build-up over months without cleaning |
| Standing water left in the machine between uses | Common | Worse if the machine goes unused for several days |
| Blocked or dry drain trap in household plumbing | Occasional | Smell present even right after a wash, not just before |
| Garbage disposal sharing the same drain line | Occasional | Disposal itself also smells; shared drain path |
How to clear it
- Remove and clean the filter assembly thoroughly
Both the coarse and fine filters, if your model has both, should twist or lift out for cleaning. Rinse under a hot tap and scrub away any film or trapped debris with an old toothbrush. This is where the smell most often originates.
- Check the recess underneath the filter
Debris collects in the housing below the filter itself, not just on the filter mesh. Wipe this area out by hand or with a cloth.
- Run a hot maintenance cycle
Empty machine, hottest setting, with a dishwasher cleaner or a bowl of white vinegar placed upright on the top rack. This reaches the sump and drain hose in a way that filter cleaning alone does not.
- Check the door seal
Food residue and moisture can also collect in the door gasket, similar to a washing machine seal. Wipe it down as part of the same cleaning session.
- Run the machine regularly
A dishwasher that sits unused for several days with a damp interior develops odour faster than one used regularly. If you are away or using it infrequently, an occasional empty rinse cycle helps keep things fresh.
When it is your plumbing, not the machine
If the smell is present even immediately after a wash cycle, rather than building up between uses, or if it smells specifically like sewer gas rather than decomposing food, the cause may be in your household plumbing rather than the dishwasher itself — most commonly a dry trap in the drain line, similar to the mechanism covered in our washing machine smells guide. Running the tap or the dishwasher regularly keeps a trap’s water seal topped up and can resolve this on its own.
If you have dealt with a musty washing machine before, this is a genuinely different smell profile — dishwashers lean toward a food-decomposition or drain smell, while washing machines lean toward a musty, mildew smell from biofilm. The cleaning approach differs slightly as a result, with more focus on the filter and sump for a dishwasher.
Keeping it from coming back
- Clean the filter every one to two weeks with regular use, not only when a smell appears.
- Run a hot maintenance cycle monthly.
- Scrape heavy food debris off plates before loading, rather than relying entirely on the filter to catch it.
- Leave the door slightly ajar between uses so the interior can dry out rather than sitting damp.
