When one unit reports an odor, start with that unit’s dry traps, washer standpipe, toilet seals and branch piping. A shared stack, vent or pressure problem can still affect only one unit. Map the complaints and have persistent odors investigated rather than assigning the cause from the number of reports.
Why one unit and not the others
Shared parts of the plumbing, like the drain stack and the building sewer, serve many units. A fault there tends to be noticed in more than one place. A single-unit report helps focus the first checks but does not rule out shared piping or ventilation problems.
The usual suspects, in order
- 1A dry trap. Every drain has a P-trap that holds a water seal. The 2024 International Plumbing Code, as adopted in Phoenix, Section 1002.4, calls for a seal of 2 to 4 inches. A second bathroom, a tub nobody uses or a floor drain by the water heater can evaporate dry in weeks in Arizona's heat. Run water in each one for a minute.
- 2The washer standpipe. The trap behind the washing machine loses its seal if the washer is not used, or if the standpipe is too short or missing a trap.
- 3A failed toilet seal. A bad wax ring can let gas up around the base. It usually comes with a wobbly toilet or stains at the floor.
- 4A tub or shower drain with a cracked trap. Look for damp spots and a smell that gets stronger when the fan is off.
- 5A fixture that lost its vent connection. Slow drains and gurgling with the smell point here.
What the manager can do fast
Send a maintenance tech to run water in every drain, then wait a day. If the smell is gone, note which trap was dry and add it to the vacancy and rotation checklist. If it returns, the unit needs a plumber to check the toilet seals, the branch vent and the trap arms.
When it is not one unit after all
If another unit reports the odor, expand the investigation to the shared stack, vents and drainage. The complaint pattern is a clue, not proof of a specific defect. Our guide to sewer smell in an apartment building covers that path.
Safety note
Sewer gas carries hydrogen sulfide. Smell alone does not measure exposure or establish safety. NIOSH warns that the sense of smell can become fatigued and cannot be relied on to warn of continuing hydrogen sulfide exposure. If a resident has headaches, nausea or asthma trouble, have the resident leave the affected area first and seek appropriate help. HQ can help 24/7, and estimates are free with upfront pricing before work starts.