Usually not in the Valley. Tempe, Scottsdale and Mesa each require a full grease interceptor, not a small grease trap, for any facility installing a commercial dishwasher. Traps are limited to kitchens with four or fewer food prep fixtures, and dishwashers push the requirement up to a gravity interceptor.
What the three cities say
- Tempe. Its FOG page says that if you have a commercial-grade dishwasher, you must install a grease interceptor to accept its wastewater. It repeats the rule for interceptors: install one when a facility uses a commercial-grade dishwasher.
- Scottsdale. Code Section 1003.3.5.1 allows hydromechanical traps only with four or fewer food prep fixtures, and only one trap size (50 gal / 100 lb), and states that any facility installing a dishwasher shall install a gravity grease interceptor. Section 1003.3.1 also lists dishwashers among the equipment that must drain to the interceptor.
- Mesa. Code 8-4-22 allows grease traps only with four or fewer food prep fixtures and says any facility installing a dishwasher shall install a grease interceptor. Its sizing table counts a dishwasher as double size.
Why dishwashers get treated differently
A dishwasher dumps a large volume of hot water, soap and food residue at once. A small trap holds water only briefly. The usual worry is that the surge flushes grease straight through instead of letting it float and separate. Heat is part of it too, since Scottsdale's code bars wastewater above 140 degrees F from entering an interceptor, so plan the connection and any cooling accordingly.
What this means for your build-out
- 1Count fixtures first. A three-compartment sink counts as one fixture, not three, in Scottsdale and Mesa.
- 2Add the dishwasher and it's an interceptor. That means outdoor space, a trench and a city permit. Interceptor minimums are 500 gallons in Tempe and Mesa. Tempe's page tops interceptors out at 2,500 gallons.
- 3Check the health side. Maricopa County also requires a three-compartment sink alongside a commercial dishwasher, and a 75-gallon water heater. See Maricopa County restaurant plan review plumbing.
- 4Sizing. Read what size grease interceptor a restaurant needs.
If you're taking over an old retail space, that's a bigger job than it looks, since the slab may have no grease line at all. Our commercial tenant improvement plumbing page covers what to check first. Tempe pump-out rules are in how often a Tempe restaurant must clean its grease trap. HQ gives free estimates before any commercial kitchen work.