Restaurant Smells Like Sewer? Find It With Smoke

A restaurant has more openings to the sewer than most buildings, and many of them are in constant use. Floor drains in the kitchen and dish room, floor sinks that catch equipment drains, mop sinks, hand sinks, restroom fixtures and the grease interceptor all connect to the same drain system, and each is a possible path for sewer gas.

The plumbing code's defense against that gas is the trap seal, a standing 2 to 4 inches of water in each trap. That water evaporates. A floor drain in a storage room or a floor sink that only gets water when a piece of equipment drains can dry out over days. Code says a seal subject to evaporation has to be protected, usually with a trap primer. If it has not been, the smell comes straight up. See why a restaurant smells like sewer and trap primers for commercial floor drains.

A smoke test tells you which of the possible causes it is, without opening floors. Here is what each result means in a restaurant:

• Smoke from a floor drain or floor sink. The trap was dry, or the seal is bad. This is the simplest fix: restore the seal, and add a primer if it keeps drying out.
• Smoke from around a drain or the base of a fixture. A leaking connection or a failed seal around the pipe.
• Smoke from a wall, ceiling or floor. A crack or open joint in the drain or vent pipe above or below. This is the case a trap fix will not cure.
• Smoke at the grease interceptor lid or its connections. The tank is open to the kitchen air. Phoenix says gravity interceptors are generally installed outside so their gases stay out of the building, so smoke at an indoor lid is worth following.
• Smoke at the ground outside. A break in the lateral or a cap missing at a cleanout. A camera confirms it, since EPA notes the surface point is not always the leak.

HQ uses liquid-smoke equipment that forces air into the vent system, not a smoke bomb with a shop vacuum. Before the smoke goes in, every floor drain and floor sink gets water, including the ones nobody remembers, so smoke shows leaks and not just empty traps. We note every drain that was dry. That list is often the whole answer.

Plan the test around your hours. After close or before opening is best, because smoke should not be near open food and staff need notice. Tell your alarm company, since smoke in a kitchen can set off detectors. HQ does not work on fire systems, so that notice is yours to give. See whether smoke tests set off fire alarms.

Under the FDA Food Code adopted in Maricopa County, a plumbing system must be repaired according to law and kept in good repair, and sewage must go through an approved system that is maintained and operated according to law. An odor that points to a failed trap or a cracked pipe is also a compliance problem. ATSDR notes that people usually smell hydrogen sulfide at very low concentrations, so a guest can notice it before you find the source.

Before you book anything, rule out gas. A natural gas leak has its own smell, and a gas leak is an emergency handled by leaving the building and calling your gas utility. See gas smell in a restaurant: leak or sewer gas. Grease interceptors have their own odor. If it rises when the tank is full, pumping and cleaning is the fix. See grease trap smell: is it full.

If one floor drain is clearly dry, pour water in it and see if the smell stops. If a drain is slow and gurgling, you have a stoppage, not a vent problem, and a cable or jetter is the tool. If the smell started right after a grease trap service, check the lid and the cleaning first. A smoke test earns its place when the smell is general, keeps returning or has a source you cannot find. For the full diagnostic order, see commercial sewer odor diagnosis.

Tell us when the smell is worst and where. HQ offers 24/7 emergency service, free estimates and an upfront price before any work starts. See smoke testing, restaurant plumbing and sewer camera inspection, and the restaurant sewer camera inspection page if smoke points to the lateral.