The short answer: Much foodservice equipment can't drain directly into the sanitary system — it must drain indirectly, through an air gap into a floor sink or floor drain, so that a sewer backup can never contaminate food, ice, or food-contact equipment. Under the IPC, equipment like sinks used for food prep, ice machines and ice bins, dipper wells, steam kettles, dishwashers, and refrigerated case condensate typically discharges through indirect waste with a visible air gap above the floor sink's flood rim. The air gap — a physical vertical separation between the drain line and the receptor — is the protection: it makes back-siphonage of waste into clean equipment impossible. Floor sinks located under or near equipment, with proper air gaps, are a core part of any compliant foodservice plumbing layout.
Why indirect waste exists
A direct drain connection means a sewer backup could push wastewater up into the equipment. For anything touching food, ice, or potable water, the code prevents that with indirect waste: the equipment drains into the open, into a receptor (floor sink/floor drain) that is itself connected to the sanitary system, with an air gap in between. Contamination can't travel backward across an air gap.
What typically requires indirect waste
Food-prep and warewashing sinks (commonly via air gap or air break).
Ice machines and ice storage bins (ice is food).
Dipper wells, steam kettles, steamers.
Dishwashers (per equipment and code).
Refrigerated case condensate drains.
Other food-contact or potable-connected equipment.
The air gap
An air gap is a vertical, unobstructed physical separation between the equipment's drain outlet and the flood-level rim of the receptor — generally at least twice the effective diameter of the drain (and not less than a minimum dimension). It must be visible and maintained. An "air break" (drain terminating below the rim but above the trap seal) is a lesser separation used where the code permits it; air gap is the stronger protection.
Floor sinks and receptors
Floor sinks are the receptors that catch indirect waste. They're located to serve the equipment above/around them, sized for the discharge, and kept accessible. Each receptor is trapped and vented per the IPC.
Common review comments
Equipment drained directly that requires indirect waste.
Missing or inadequate air gap (or an air break where an air gap is required).
Floor sinks not shown, mislocated, or insufficient for the equipment served.