Are garbage disposals allowed in Phoenix-area restaurants?

• Phoenix: disposals are not banned, but they force the equipment up. No food waste disposal unit can discharge to a hydromechanical trap. A kitchen with one needs an outdoor gravity grease interceptor, regardless of fixture count.
• Tempe: its inspection list says garbage disposals or food grinders are not permitted.
• Mesa: except for domestic sources, users may not install or replace equipment that turns garbage or solid waste into liquefied waste and sends it to the sewer through a garbage grinder or disposal. Garbage and solid waste go out as solid waste.
• Chandler: its food service page says the plumbing code does not let a food waste disposer or grinder discharge to a FOG treatment device. It cites Section 1003.3.2 of the 2018 International Plumbing Code, so confirm the current section with the city.
• Surprise: its sizing formula multiplies by 17 instead of 12 when a disposal is used.

A disposal sends ground food solids into the grease line along with the water. Phoenix sizes a gravity interceptor with a 17-minute retention time when there is a garbage disposal, rather than 12, and Surprise's formula multiplies by 17 instead of 12 when a disposal is used.

Phoenix's kitchen practices: scrape or dry-wipe pots, pans and utensils into the trash, and put removable screens on every kitchen drain. Clean the screens often.

Ask the city's pretreatment office before you reconnect an old disposal, since the rules above apply at plan review and permit. If you keep one in Phoenix, expect a bigger interceptor. Our guide to interceptor sizing and what can go into a grease trap show the math and the fixture list.