Where can a grease interceptor be located?

In the cities we read, yes, unless the city approves something else. A grease trap is the small indoor unit. A gravity interceptor is the big tank, and it belongs outdoors.

• Phoenix. The FOG manual says gravity interceptors are installed outdoors. The 2024 IPC amendment says gravity grease interceptors shall be installed outside unless otherwise approved by the Authority Having Jurisdiction. The city's stated reason is that gravity interceptors are generally installed outside to prevent sewer gases and odors from entering the building.
• Tempe. The FOG program page says that because of their large size, grease interceptors are located outside the building.
• Scottsdale. Its guidelines describe gravity interceptors as located underground outside of the building.
• Surprise. Interceptors within the city shall be an outside installation.

That is why a kitchen that outgrows a trap needs yard, alley or parking space. See when a trap has to become an interceptor for the triggers.

### Are there exceptions?

Phoenix's wording leaves room. Outside is the rule unless the Authority Having Jurisdiction approves otherwise. The amendment does not list what qualifies, so any indoor plan starts with the reviewer, not the plumber.

There is also a relief valve for tight sites. Scottsdale's guidelines, which are based on its amended 2021 IPC, say that where lack of space or other constraints prevent the installation or replacement of a grease interceptor, one or more interceptors are permitted on or above the floor and upstream of an existing interceptor. Phoenix's 2024 amendment deleted that relief. The city's stated reason is that installing interceptors upstream of an existing interceptor "does not increase the flow capacity of the existing grease interceptor." In Phoenix, ask the city before planning around it. Where it is allowed, it adds capacity in front of a tank you already have. It is not a way to skip the outdoor tank in a new install.

Every city that speaks to this says the same thing in different words.

• Phoenix City Code 28-13, reprinted in the FOG manual, says all interceptors must be located as to be free from obstructions, and readily and easily accessible for cleaning and inspection.
• Mesa's code 8-4-22 says all interceptors shall be located as to be readily and easily accessible for cleaning and inspection.
• Gilbert's code says all pretreatment devices shall be easily accessible for cleaning and inspection, and that grease removal devices are installed on the premises where grease is used or generated.
• Surprise lists accessible for cleaning and inspections among its interceptor requirements.
• The model plumbing code says access shall be provided to each interceptor and separator for service and maintenance (Section 1003.10). Scottsdale's guidelines carry the same line.

Two practical points follow from that.

First, the lid is what people reach, so what sits on top matters. A tank under a dumpster pad, a planter or a parked-car stall is not free from obstructions. Phoenix's manual also says that if an interceptor is in a potentially hazardous location, such as active traffic locations, the Director reserves the right to temporarily close the area to traffic to allow inspection. Surprise asks for appropriate traffic rated covers. Our page on traffic-rated lids covers that choice.

Second, Phoenix sets a minimum manway size. Its amendment says all man-ways shall have a minimum 20 inch inside diameter. A 500 gallon unit needs two compartments and two man-ways, and units of 750 gallons and larger need two compartments and three.

The codes we read do not set a maximum distance. We looked at Phoenix, Tempe, Mesa, Scottsdale, Gilbert and Surprise and found no number of feet. Slope, cleanouts, property lines and the sewer connection decide it, and the plan reviewer confirms.

Slope is the real limit. Phoenix's amendment says that where drainage piping is upstream of a grease interceptor, the slope shall be not less than 1/4 inch per foot. Mesa's plumbing checklist says the same for grease waste lines. Do the arithmetic and you see the problem. A 40 foot run drops 10 inches at that slope. The pipe keeps falling the whole way, so a long run on a flat lot means the tank inlet ends up lower in the ground.

Venting also shapes the location, since interceptors must be designed so they do not become air bound. See does a grease interceptor need a vent.

Four things beyond distance: sharing, easements, tank size and the manufacturer's sheet. Then a short checklist.

### Can two restaurants share one tank?

Usually not. Scottsdale's guidelines say interceptors shall be single-user only. Surprise is different for small setups and says: No more than 2 restaurants per interceptor with under sink trap units installed. That wording is short, so ask the city what it means for your layout. Strip centers raise the question often, and shared interceptors in strip centers works through it.

### What about setbacks and easements?

Scottsdale asks for site and civil drawings when a gravity interceptor is required, and says to show all setbacks and PUEs, meaning public utility easements. Check the site plan before you sign a lease, because the only open spot may be one the drawings will not allow. Trenching that crosses the public right of way brings its own rules, covered in permit to dig in the right of way in Phoenix.

### Does the size change the location?

It can. Mesa and Tempe cap interceptors at 2,500 gallons. Surprise says two smaller interceptors are required once the size reaches over 2500 gallons. Scottsdale's worksheet notes that standard pumping trucks have a 2500 gallon limit, so a larger tank needs a special truck or several. Two tanks means two locations, two sets of lids and two service points. The sizing walk-through shows how to see that coming.

### What does the manufacturer say?

Phoenix's amendment says the size, type and location of each interceptor shall be designed and installed in accordance with the manufacturer's instructions and the requirements of the Authority Having Jurisdiction. Get the instruction sheet for the exact model early. It lists what the tank needs around it.

### What should you do before you pick a spot?

1. 1Mark the kitchen fixtures that drain to grease and where they leave the building.
2. 2Walk the outside with the plumber, looking for a spot with clear access to the lids.
3. 3Check for utility easements, setbacks and traffic. Ask for the lease site plan.
4. 4Confirm the slope from the kitchen to the tank works at the depth you need.
5. 5Ask the plan reviewer to approve the location before trenching. Our permit page explains who reviews it, and the installation steps show where location fits in the schedule.

A broken outlet tee or baffle is a separate problem from location. See what happens when a baffle or outlet tee breaks.

Call one before you sign a lease or order a tank. A licensed plumber can walk the site, check slope and depth, and flag conflicts before anyone digs. HQ is licensed and insured and gives free estimates with the price set up front. If a commercial line backs up while you wait, our 24/7 emergency service is there. Start on the commercial plumbing page.

Peoria also requires a sample vault on outdoor interceptors, and other cities can ask for one; see grease interceptor sampling ports.