Sewage odor indicates drain backflow, a missing high loop or air gap, a dry/blocked trap or household plumbing problem more than ordinary tub residue. Run the sink and disposal with the dishwasher idle and watch whether dirty water shows in the tub.
What this covers
- Dishwashers · drain plumbing
What it does not cover
Differential
Likely causes of “Dishwasher smells like sewage”, and how to tell them apart
- 1
Drain water is backing up from the sink or disposal
What separates it The smell is strongest at the sink and disposal, and gray water appears in the tub after the sink drains.
How to confirm Run the sink and disposal with the dishwasher idle and watch whether dirty water shows in the tub.
- 2
The high loop or air gap is missing or set wrongly
What separates it Wastewater siphons back into the tub, and the drain hose runs low under the counter instead of up.
How to confirm Look under the sink at how the drain hose is routed; it should rise to the underside of the counter or connect through an air gap.
- 3
A dry trap or a blocked household drain
What separates it Other drains in the house smell as well, and a fixture that is rarely used has a dry trap.
How to confirm Run water in the unused fixtures for a minute and see whether the smell fades.
- 4
Rotting food in the filter or sump
What separates it The smell is rotten and sour rather than sewer-like, and it is strongest when the filter is lifted out.
How to confirm Remove the filter and smell it on its own, then rinse it.
Before you touch a setting
Record this first — changing settings destroys the evidence
- Where the smell is strongest: at the door, at the sink, under the sink or from other drains.
- Whether the smell follows use of the disposal or the sink.
- Whether dirty or gray water appears in the tub after a cycle.
Try in this order
0 of 4 completedObserve before changing anything
ReversibleCheck whether odor is strongest at the sink/disposal and whether dirty water appears in the tub after sink use.
Isolate the failing boundary
ReversibleInspect the high loop, air gap and disposal connection and have the household drain and vent checked.
Apply the narrow correction
ReversibleCorrect plumbing first, then clean the filter and run an approved maintenance cycle.
Verify the result and stop at the boundary
ReversibleStop for wastewater backup or leakage beneath the sink or dishwasher.
Stop boundary
When this stops being a self-service repair
- !Stop for wastewater backup or leaks under the sink or beneath the dishwasher; call a qualified plumber for the household drain and vent.
Evidence ledger
Sources behind this answer
Exact questions
Common questions
Does a sewer smell mean the dishwasher is broken?+
Not usually. It more often points at the drain connection, a dry trap or a household drain problem, so correct the plumbing before cleaning the machine.
Does a sewer smell always mean a drain problem?+
Often it is a clogged filter or a drain line that lets sink water flow back. Clean the filter, run the sink disposal and check that the drain hose loops high under the counter or passes through an air gap.
What does the drain hose loop do?+
It keeps sink water from running back into the tub. A hose without a high loop or an air gap lets dirty sink water and odor back in.
Why does it smell like sewage?+
A dry trap, missing high loop or drain problem can let sewer gas back.
Should I run water in the sink?+
Run water to fill the trap and check the drain hose.
When is it a plumbing problem?+
If other drains smell too, call a plumber.