Car Wash Plumbing in Phoenix and the Valley

Wash water carries sand, grit, oil and soap, and Valley cities want it to pass through an interceptor before it reaches the sewer. Phoenix City Code 28-12 names carwashes alongside service stations and auto repair shops, and Mesa City Code 8-4-22 does the same. Gilbert says it outright: no wash rack water goes to the sewer without a pretreatment device.

The 2024 International Plumbing Code, one of the two plumbing codes Phoenix lets designers use (the UPC is the other), backs this up. It requires oil separators at car washing facilities. A separator can be listed and labeled, or designed to the code, and a designed one is sized by drained floor area: at least 6 cubic feet for the first 100 square feet, plus 1 cubic foot for each additional 100 square feet. The IPC also says wastes that don't need separation can't go into an interceptor or separator, and Phoenix's amendment to that section puts the authority having jurisdiction in charge of approvals. Restrooms and break-room sinks stay on their own line.

Mesa's code sets the minimum interceptor at 500 gallons and the maximum at 2,500 gallons, with at least two chambers. Phoenix keeps a list of approved interceptors and requires every interceptor to sit where it's free of obstructions and easy to reach for cleaning and inspection. If yours is under a vacuum island or a parked equipment trailer, that's a problem before it's ever full. The Phoenix interceptor rule page walks through who has to have one.

Phoenix sets two limits for gravity interceptors that don't serve food. Pump and clean it before grease, oil, sand, sludge and solids reach 25 percent of the liquid volume, and never go longer than 12 months without a full pump-out unless the city grants a variance. A busy tunnel fills far faster than that, so the 25 percent line usually sets your real schedule.

Scottsdale sets its own floor: car washes pump and clean at least once a year, more often if the volume calls for it. Both cities want the records (pump-out invoices included) on site for three years, and Phoenix spells out what they should show: volume removed, device capacity, disposal, repairs. The removed contents can't be decanted back into the interceptor or a cleanout either.

Here's the play: log every pump-out, measure the sludge between visits, and shorten the interval if it's climbing past a quarter full. The Chapter 28 program page has the rest of the city's rules.

Car wash equipment mixes city water with soaps, waxes, spot-free rinse systems and, often, reclaim water. That's a textbook cross-connection. Phoenix lists carwash facilities for an air gap or a reduced pressure (RP) assembly, and Mesa requires an RP assembly (it calls it an RPA). In Phoenix every assembly is tested at least once a year by a certified tester, with the results filed with the city and kept for three years.

If the assembly fails, the customer has to repair or replace it and retest. In Phoenix, a repair has to be done by a certified repairer following ASSE Standard 5130. HQ tests and certifies domestic backflow assemblies, files results with the city, repairs leaking assemblies and replaces stolen ones. Fire backflow assemblies and fire sprinkler system work are outside what HQ does. See RPZ vs double check and why an RPZ spits water.

Many washes reuse part of their water, and Gilbert's code says outright that its pretreatment rule doesn't block proper reuse. Reclaim tanks and pits still collect sludge that needs pumping, and the lines between them clog like any other drain.

What can't happen is wash water leaving the site through the storm drain. Phoenix allows only stormwater into public storm drains and retention basins, with a short list of exceptions. Individual residential car washing is on that list. A commercial wash is not.

New washes get paperwork up front. Chandler requires every non-residential user, truck and car washes named, to submit a Wastewater Discharge Questionnaire before discharging to the sewer. Phoenix requires a permit from its Planning and Development Department to install any backflow assembly; see what plumbing work needs a permit.

We jet bay drains, trench drains and reclaim lines with hydro jetting, camera and repair the sewer lateral, replace failing interceptor tees and piping, install water heaters and gas lines, and provide backflow testing, certification, city filing, leak repairs and assembly replacement. We're available 24/7, and you get an upfront price before work starts. Most drain work can be scheduled before opening so the tunnel keeps running.