Find out whether the smell is in one unit, one floor or the whole building, then check the usual suspects in that order: dry traps in vacant units and laundry rooms, common floor drains, and roof vents. Log every complaint. A smell that spreads across floors points to a stack, vent or main line problem.
Step 1: Map where the smell is
Walk the building with the complaint list in hand and mark each spot on a floor plan. Three patterns cover most cases.
- One unit only: start with that unit’s fixtures and branch piping, while keeping shared-system causes in the investigation. See why only one unit smells like sewer.
- Same spot on several floors, stacked above each other: the shared drain stack or its vent. That is a building-side problem.
- Ground floor, laundry room, garage or trash room: floor drains and the lowest part of the drain system.
Step 2: Check the traps first
Every drain holds a water seal in its P-trap. The 2024 International Plumbing Code, as adopted in Phoenix, Section 1002.4, requires each fixture trap to hold a seal of not less than 2 inches and not more than 4 inches, and Section 1002.4.1 says seals subject to evaporation must be protected, for example with a trap seal primer. In Phoenix heat a seal in a vacant unit's guest bath, a laundry floor drain or a pool-equipment room can evaporate and let the smell in. Run water in every fixture and floor drain in the affected area. If the smell fades, you found it.
Step 3: Look at vents and the main line
If traps are full and the smell comes back, look at the roof vents for debris, bird nests or damage, and look for slow drains or gurgling. A plumber can then camera the stack and the main. A blocked vent can pull water out of traps as fixtures drain, so full traps that keep emptying point there.
Step 4: Know what the law asks of you
For residential tenants, Arizona's landlord-tenant act requires the landlord to keep plumbing and sanitary facilities in good and safe working order (A.R.S. 33-1324). Treat a traced plumbing fault as a repair you owe, not a courtesy.
Step 5: Keep a record
Log each complaint with date, unit, what was smelled and what you did. The EPA's building air quality guide includes complaint and incident logs for exactly this. Our odor complaint log checklist gives you one to copy.
When to stop DIY checks
Do not rely on your nose to judge safety. ATSDR notes that people can lose their sense of smell after minutes at higher hydrogen sulfide levels. A strong smell, or residents with headaches, nausea or breathing trouble, means clear the area and read the first signs of sewer gas exposure. HQ offers 24/7 emergency service, is licensed and insured, and gives free estimates and upfront pricing if you need a plumber to trace a stack or main.
A smoke result identifies an air path under the test conditions. Obstructions, soil and concealment can limit visibility, so no visible smoke does not rule out every defect. The crew confirms the cause before assigning a repair or responsibility. See HQ’s plumbing smoke testing.
For a related odor investigation, see sewer smell in an office restroom: how do you trace it.
For a related odor investigation, see sewer smell in a strip mall: how do you find which tenant.