12.1 Indirect Waste

12.1 Indirect Waste

Quick Answer: Under 248 CMR 10.12 (effective 12/8/2023), an indirect waste pipe does not join the building drain. It dumps into a properly trapped and vented receptor through an air gap or an air-break. The air gap is at least twice the effective diameter of the drain served. Never trap the indirect waste ahead of that gap or break. Food-service refrigerators, ice machines, steam tables, and similar equipment are indirect. Pot sinks, scullery sinks, hand-washing sinks, and dishwashing pre-rinse sinks installed with a commercial dishwasher are direct. Size the receptor one pipe size larger than the largest indirect waste. Keep receptors out of toilet rooms and closed, unventilated spaces. This is plumbing drainage, not a Type B gas vent.

The PSI Candidate Information Bulletin dated October 3, 2025 lists Indirect Waste inside the Drain, Waste & Vent written cluster. Massachusetts writes the rule in 248 CMR 10.12, not in IPC Chapter 8. Candidates who grew up on a 15-foot developed-length slogan, a one-inch drainage air-gap floor, or “every kitchen fixture is indirect” will miss items that 10.12 already decided. Independent OpenExamPrep teaching for the Massachusetts journeyman plumber exam uses the 12/8/2023 Uniform State Plumbing Code.

248 CMR 10.03 defines the two separations. An air gap (drainage system) is the unobstructed vertical distance through free atmosphere between the waste-pipe outlet and the flood-level rim of the receptor; that gap shall be at least twice the effective diameter of the drain served. An air-break is a piping arrangement that discharges below the flood-level rim of the fixture, receptacle, or interceptor. An indirect waste pipe never connects directly with the drainage system; it reaches a wasted and vented trap, fixture, receptacle, or interceptor through one of those two openings.

Food equipment that must be indirect — and the sinks that must not

248 CMR 10.12(1)(a) is the food-and-beverage list. Establishments that store, prepare, sell, serve, or process food provide indirect waste piping for refrigerators, refrigerator coils, walk-in freezers or coolers, ice compartments, ice-making machines, steam kettles, steam tables, potato peelers, egg boilers, coffee urns, coffee, soda and beverage trays, and similar equipment. In places that serve soda and alcohol, individual sink compartments that store ice discharge independently into a floor drain or floor sink.

Then 10.12 flips the switch. Dishwashing pre-rinse sinks installed in combination with a commercial dishwasher, pot sinks, scullery sinks, hand-washing sinks, and similar shall not be indirectly wasted. They are directly connected to the sanitary drainage system. A Worcester kitchen that air-gaps the three-compartment pot sink “because food is in the room” is the classic wrong installation.

Culinary or produce compartments are a third pattern. A single-compartment sink, or an individual compartment of a multi-bay sink, used for culinary or produce work discharges individually into a properly vented floor sink or floor drain. Label that compartment with a laminated sign in two-inch letters: “This Compartment ONLY Is Designated for Produce Preparation.” 10.12 Example 1 is the Board’s picture. Do not let a produce bay share a tailpiece with a pot-wash bay and call the whole sink “indirect.”

All indirect waste discharges through an air gap or air-break into a properly trapped and vented receptor (10.12(1)(a)5 and Example 4). An air gap is required if the indirect waste pipe is under vacuum. Food-service vacuum drainage follows the equipment manufacturer’s instructions or a Massachusetts professional engineer design. Plastic pipe and fittings are allowed within ten feet of the equipment, or above the equipment served, before transitioning to commercial materials (10.12 Example 2). That ten-foot figure is a material-transition length, not a license to hide an inaccessible indirect main.

Scenario. A Boston restaurant has a gravity dishwasher five feet from a vented floor-drain trap, a three-compartment pot sink, and an ice machine. The ice machine is indirect. The pot sink is direct. The dishwasher may use the inlet side of that floor-drain trap because it is within five feet; if the machine is eight feet away, go back to an indirect receptor. Do not invent a “everything in the kitchen is air-gapped” rule.

Air gap versus air-break, potable tanks, sterilizers, and the trap ban

248 CMR 10.12(2) repeats the opening rule for every indirect waste: discharge into the building sanitary or storm system through an air gap or air-break as stated in 10.12(1)(a)5, and in no instance shall the indirect waste be trapped ahead of the air gap or air-break. A P-trap on the ice-machine tailpiece before the floor sink is the violation. Traps belong on the receptor, not on the open indirect line in front of the gap.

Methods of providing an air gap (10.12(2)(a), Example 5 Drawing 1). The gap is at least twice the effective diameter of the drain served, by one of two routes:

1. To a receptor. Extend the indirect waste to an open, accessible individual waste sink, floor drain, or other fixture that is properly trapped and vented.
2. To the inlet side of a trap. Provide the air gap in the drain connection on the inlet side of the trap that receives that waste.

Air-break (10.12(2)(b), Example 5 Drawing 2). The outlet extends below the flood-level rim of the receptacle. 10.12 sends the numeric picture to that drawing rather than printing a one-inch UPC slogan in the text. Teach the geometry: an air-break is still a physical separation, but the pipe is in the receptor, below the rim. It is not a substitute when 10.12 requires an air gap (vacuum lines; water-distribution drains, overflows, and relief lines; sterilizers).

Water-distribution and potable tanks (10.12(1)(b) and (f)). Drains, overflows, or relief lines from the water distribution system get an air gap — not an air-break. Safe waste pans go under water heaters, storage tanks, or boilers that store six gallons or more and sit elevated above any occupied space. Pipe the pan indirectly to a trapped and vented fixture or to a point within 12 inches of the lowest floor level. Minimum waste pipe is one inch. Pans are at least two inches deep with two inches of clearance around the appliance base. Same-floor floor drains or other acceptable indirect points remove the pan requirement. On a replacement heater, tank, or boiler, a Product-accepted automatic shut-off plus a pan without drain piping is an acceptable alternate; the temperature-and-pressure relief valve then discharges into that pan. Discharge piping materials follow 248 CMR 10.06 for the occupancy.

Sterilizers (10.12(1)(c)). Stills, sterilizers, and similar apparatus used for sterile materials are indirectly connected by an air gap. Hospital sterilizer details continue in 248 CMR 10.18; the 10.12 exam fact is air gap, not a sanitary tailpiece. Drips and drainage outlets (10.12(1)(d)) may use an air gap or an air-break into an open receptacle.

Clear water (10.12(1)(e)). Cool the waste to no greater than 150°F before it hits storm or sanitary. Expansion tanks, fire-sprinkler drains, air-conditioning equipment, drip or overflow pans, and similar clear-water-only devices discharge to the building storm system through an air gap or air-break. The flood-level rim of that indirect fixture is a minimum of two inches above floor level. A trap vent on that storm connection is labeled “storm vent” at least every ten feet, at direction changes, and on each side of a partition, wall, ceiling, or roof penetration. Three published exceptions let some clear water reach sanitary: written authorization from the authority whose system will take it; safe-waste-pan discharge to a trapped, vented sanitary fixture; and condensate (or hydrocarbon-free compressor blow-down) of 12.5 gallons per hour or 300 gallons per day or less. No steam condenser waste pipe connects directly to sanitary or storm, and water above 150°F does not enter either system (10.12(4)).

Receptors, trap rules, and the length limits 10.12 actually prints

Receptors (10.12(3)). Do not set indirect-waste receptors or sumps in toilet facilities or in an inaccessible or unventilated closet, storeroom, or crawl space. The pipe serving a receptor is a minimum of one size larger than the largest indirect waste it serves. A receptor set below floor level gets a running trap adjacent to it with the trap cleanout brought level with the floor. Every receptor has a readily removable metal basket under the discharge, or a beehive strainer not less than four inches in height. Size and design the receptor so the discharge does not splash or flood the floor. No domestic or culinary fixture is a receptor, except in a residence a kitchen sink may receive dishwashers and portable clothes washers when that kitchen-sink drain is a minimum of two inches.

Installation and length (10.12(5)–(6)). Indirect waste piping is installed so it can be flushed, cleaned, or replaced. A fixture or appliance whose waste outlet is smaller than 1¼ inches connects to an indirect waste one size larger than that outlet. Massachusetts does not print an IPC-style 15-foot developed-length cap in 10.12. What it does print:

• Individual indirect waste: one outlet to the receiver.
• Branch: one outlet to a main or branch main.
• Main: more than one outlet to the receiver.
• Branch main: a branch from a main that itself serves more than one outlet.
• No trap on an indirect waste main or branch main. A trap may sit on a branch or individual line when you need to stop air from blowing back through that branch. When that branch is trapped, install a properly sized vent.
• Air must circulate freely through an individual waste, a waste main, or a waste branch main.
• An indirect waste stack that receives fixtures on two or more floors extends to the outer air as required for a stack vent.
• In a central system serving more than one tenant, each occupancy’s branch is trapped as a secondary indirect waste receiver. Indirect-waste vents do not join any other venting system; they run separately to the outer air as stack vents do.

Scenario. A two-story market ice-machine stack that also picks up a first-floor walk-in cannot die into a basement floor sink without a stack-vent extension. A ten-inch crawl-space floor sink under a restaurant is both inaccessible and unventilated — move the receptor. A 1½-inch ice-machine waste into a 1½-inch receptor drain fails the one-size-larger rule.

Do not size, trap, or “except” indirect waste from an IPC Chapter 8 memory. Air-gap multiples, the pot-sink direct connection, the two-inch residential kitchen-sink receptor, the five-foot commercial dishwasher option, and the no-trap-ahead-of-the-gap rule live in 248 CMR 10.12 and the companion dishwasher paragraph in 10.10(7).

Official resources

• 248 CMR 10.12 Indirect Waste Piping (Cornell LII) — 12/8/2023 air gap, food equipment, receptors, traps
• 248 CMR 10.03 Definitions (Cornell LII) — air gap, air-break, indirect waste pipe
• 248 CMR 10.10(7) Dishwashing Machines (Cornell LII) — commercial gravity five-foot floor-drain option
• 248 CMR 10.00 Uniform State Plumbing Code (Mass.gov) — official 12/8/2023 posting