Grease Trap and Interceptor Rules by Valley City

Maricopa County Environmental Services reviews every new restaurant's plans, but it hands grease devices to the cities. Its construction guide says "Local municipalities determine the number and size of grease traps, grease interceptors or catch basins." That one line is why this page exists: the health inspector checks that a trap can be reached for service, and the city decides what trap you need, how big, and how often it gets pumped.

The city rules live in two places:

• The sewer or pretreatment chapter of the city code (Phoenix Chapter 28, Mesa 8-4-22, Glendale 33-238, Gilbert 66-244). This is where pumping intervals, records and additive bans sit.
• The city's plumbing code. Most Valley cities enforce the International Plumbing Code: the 2024 edition in Phoenix, Mesa, Tempe, Chandler, Glendale, Surprise, Buckeye and Tolleson, the 2021 edition in Scottsdale, and 2018 in Gilbert and Peoria. Phoenix also lets designers use the 2024 Uniform Plumbing Code. Several cities add a four-fixture limit on grease traps, either in their plumbing code amendments (Scottsdale) or their sewer code (Mesa).

Six terms decide how these rules apply to your kitchen, and the city codes use them without much explanation.

• Grease trap (hydromechanical grease interceptor). A small unit, usually indoors under or near the sinks, rated by flow and grease capacity (for example 50 gallons per minute and 100 pounds).
• Gravity grease interceptor. A large tank buried outside, rated in gallons (500 to 2,500 in Mesa and Tempe). Grease floats and solids sink while the water sits.
• Fixture. The four-fixture limit counts different things in different cities. Mesa and Scottsdale count only "fixtures used for food preparation," and both say a three-compartment sink counts as one. Phoenix counts the plumbing fixtures routed to the trap, and its own example includes the mop sink. Tempe counts "kitchen fixtures (sinks, floor drains, etc.) connected to the grease waste line."
• The 25 percent rule. Clean the device before grease plus solids fill a quarter of it. Phoenix requires a full cleaning at that point; Chandler states it as its rule of thumb.
• Decanting. Pouring pumped water back into the trap to save hauling. Glendale and Scottsdale ban it outright.
• Food service establishment. The term city programs use for restaurants, bars, cafeterias, school and hospital kitchens and similar places.

They cover businesses that send greasy, oily or sandy wastewater to the city sewer, starting with commercial kitchens. Several codes also reach laundries, service stations, auto repair shops and carwashes, which need oil or sand interceptors. Surprise goes further and lists nursing homes, assisted living and group homes operating in residential zones.

These rules do not apply to a regular house. Scottsdale's code says interceptors "shall not be required for domestic users," and Surprise exempts private homes unless they're used as a care home or business.

This applies to Phoenix, Mesa, Scottsdale and Tempe, which all publish the four-fixture limit. Other cities decide case by case at plan review.

It depends on the city and the device. Here are the written minimums:

Treat these as the longest you may wait. A busy fryer kitchen can hit 25 percent in two weeks, and the 25 percent mark wins over the calendar.

The same kitchen can get a different answer in the next city, and one appliance can flip it.

A taco shop moves from Mesa to Gilbert. In Mesa its four sinks and no dishwasher allowed an indoor trap. In Gilbert the device is the plan reviewer's call, and town code sets pumping at least every six months.

A Scottsdale cafe adds a dishwasher. Three fixtures kept it on a 50 gallon trap. The dishwasher changes the answer: Scottsdale's amended IPC 1003.3.5.1 requires a gravity interceptor for any facility installing one. That's a buried tank, a plumbing permit and plan review, not an under-counter swap.

A restaurant group runs kitchens in Glendale and Phoenix. Pumping every 180 days keeps the Glendale store legal. The same schedule on a Phoenix grease trap misses the 30-day rule five times over.

An operator buys an enzyme dosing system to stretch pumping. In Chandler, Phoenix, Glendale, Peoria and Buckeye, additives cannot replace pumping. Gilbert allows them only as a supplement, after telling the town and handing over safety data sheets.

Start with the address and the fixture count, then follow the city's own sizing method and pumping rule.

1. 1Find the city that serves your sewer. Your rules follow the sewer provider at the address, not the mailing city. Fountain Hills, for example, is run by its own sanitary district.
2. 2Count the fixtures that drain to the grease line and note any dishwasher or disposal. That decides trap or interceptor in most cities.
3. 3Pull that city's sizing method. Phoenix publishes a gravity interceptor worksheet in its FOG manual, Tempe links a sizing spreadsheet on its FOG page, and Mesa's table is in City Code 8-4-22.
4. 4Submit the device on your plumbing plans with the city's building permit, alongside the county health plan review for the food establishment.
5. 5Set the pumping schedule at the shorter of the city minimum and the 25 percent mark, using a hauler that holds a Maricopa County nonhazardous liquid waste permit.
6. 6Keep every pumping, cleaning and repair record on site for three years. Phoenix, Chandler, Glendale, Scottsdale and Surprise all put that period in writing.

Most mistakes come from assuming one statewide rule.

• "The county health department sets grease trap size." It doesn't. The county's own guide gives sizing to the cities.
• "Arizona requires pumping every 90 days." There's no statewide number. The written minimums run from 30 days to 180 days, depending on city and device.
• "Enzymes mean fewer pump-outs." Phoenix bans chemicals, enzymes, bacteria, solvents and emulsifiers used to dissolve grease, and most Valley cities bar them as a substitute for pumping.
• "A small trap works for any small restaurant." Not with a dishwasher. Phoenix, Mesa, Scottsdale and Tempe all require an interceptor once one is installed.
• "Records only matter after a problem." Inspectors ask for them on routine visits. Tempe's inspection list requires pump-out records on site.

Chandler says an additive system found in a grease device must be removed at the owner's expense and that citations and fines may follow. Phoenix inspectors read the maintenance records on routine visits to see how often the interceptor really gets pumped, and Tempe checks device condition and pump-out records on every FOG inspection.

If you'd like a licensed plumber to size, install or service the device, HQ handles commercial drain and grease line work across the Valley, with free estimates.