Do commercial sinks need an air gap or indirect waste?

The 2024 International Plumbing Code, as Phoenix adopted it, has an indirect waste chapter with the rules a kitchen has to meet:

• Food handling. Equipment and fixtures used for the storage, preparation and handling of food "shall discharge through an indirect waste pipe by means of an air gap." Each well of a multiple-compartment sink must discharge independently to a waste receptor.
• Utensil, dish, pot and pan sinks. Sinks, in other than dwelling units, used for washing, rinsing or sanitizing them "shall discharge indirectly through an air gap or an air break to the drainage system."
• Commercial dishwashers. The discharge goes through an air gap or air break into a waste receptor.
• Floor drains in walk-in coolers and freezers. They connect indirectly, by an air gap.

The code sets rules for the receptor too. It has to be trapped and vented and connect to the building drain, and it needs a removable strainer or basket over the outlet (hub drains that take only clear-water waste and standpipes are exceptions). It can't be in a concealed space, crawl space, attic or above a ceiling, and it has to have ready access. It must be sized for the maximum discharge of everything draining into it, and installed to prevent splashing or flooding. The standard version in a kitchen is a floor sink, and we explain how it differs from a floor drain in floor sink vs floor drain vs mop sink.

For a walk-in unit, the cooler condensate connection checklist separates the refrigeration-unit drain from a room floor drain and coordinates the manufacturer's instructions.

How big is the gap? The code says the air gap must be not less than twice the effective opening of the indirect waste pipe. Maricopa County's plan review guide separately asks for a minimum 1-inch air gap on the three-compartment sink drain and on the prep sink, so design to whichever number is larger. If the indirect waste pipe runs more than 30 inches horizontally or 54 inches in total developed length, it must be trapped.

For a full-service restaurant, the county's plan review list includes:

• An NSF-approved three-compartment sink with its drain "indirectly plumbed with a minimum 1-inch air gap where permissible."
• A separate NSF stainless steel prep and rinse sink for defrosting food or rinsing produce, also indirectly plumbed with an approved minimum 1-inch air gap.
• A three-compartment sink whenever a commercial dishwasher is installed.
• No garbage disposal on prep, one-, two- or three-compartment sinks. A disposal may be allowed on a separate pre-rinse or scraping sink.

Mobile Type III units are the same idea in a smaller package. The county's Type III guidelines list a three-compartment sink and a wastewater holding tank. See where food trucks dump for that side.

The county's plan review says that all equipment and fixtures connected to a water supply must have an approved backflow prevention device or an air gap, and adds that "Ice machines are typically exempt." That's the supply side. The same guide doesn't spell out a waste-side rule for the ice machine drain, so ask your plan reviewer how yours should be piped before you rough it in.

• Building out a kitchen. Put floor sinks where the three-compartment sink, prep sink and dishwasher drain, and leave the space above them clear. Moving one after the slab is poured means opening the floor.
• Grease. Fixtures that drain to a floor sink may also have to reach your grease interceptor. Check that before finalizing the layout: see can a commercial dishwasher drain to a grease trap and the full Maricopa County restaurant plan review list.
• Home dishwashers. The residential version is covered in what is a dishwasher air gap.

HQ does commercial kitchen plumbing, including floor sinks and indirect waste piping, and gives free estimates before any work starts.