4.3 Indirect & Local Waste Piping, Air Gaps & Receptors

Definitions

• Indirect waste piping is drain piping that does not connect directly with the drain system. It discharges into the drain system through an air break or air gap into a receptor (SPS 381.01 (131)).
• Local waste piping receives the discharge from indirect waste piping and itself discharges through an air break or air gap into a receptor (SPS 381.01 (145)).

Indirect and local waste piping serving equipment of public health concern is plumbing (SPS 382.33 (1) (b)). Table 382.33-1 lists, among others, baptismal founts, bar and soda fountains, boiler blowoff basins, clothes washers, coffee makers, dishwashers, food preparation sinks, ice makers, refrigerated cases and rooms, steam tables, sterilizers, stills and vending machines.

Materials, size, traps and length

Air gaps and air breaks (SPS 382.33 (7))

An air gap is complete separation and gives the highest protection. An air break lets the pipe enter the receptor but keeps it above the trap outlet, so a backup overflows the receptor rather than the appliance.

Receptors (SPS 382.33 (8))

• Waste sinks and standpipes: rim at least 1 inch above the floor.
• Floor sinks: a removable metal basket or dome strainer. Waste may not discharge through a traffic grate; it must terminate over an ungrated portion.
• Local waste piping may not receive discharge from another local waste pipe.
• A plumbing fixture may serve as a receptor only in listed cases. For example: a portable dishwasher or water treatment device to a dwelling kitchen sink or branch tailpiece; a clothes washer or softener to a laundry tray; a T&P relief valve, softener, backflow device, humidifier or furnace condensate to a floor drain riser (with an air break) or to a floor served by a floor drain. In a one- or 2-family dwelling, a T&P valve or water treatment device may discharge through the cover of a clear water sump with a fixed air gap.

Required indirect connections (SPS 382.33 (9))

Boilers, pressure tanks and relief valves discharge through an air gap. Steam pipes may not connect to any part of the plumbing system. Wastewater over 160 degrees F must discharge indirectly, and steam condensate blowdown must be cooled to 160 degrees F first. Clear water discharging to the plumbing system uses an air gap.

Residential clothes washers discharge through an air break to a standpipe:

Washer waste may not go to gutters, troughs, local waste piping or indirect manifolds. A single residential ventless dryer discharging under 1 gpm may share a 2-inch washer box or standpipe. Commercial gravity-dump washers discharge by air break into a receptor or trench sized for one full simultaneous load, through a laundry interceptor.

Dishwashers. All dishwashers discharge to the sanitary system.

• Residential: indirect waste no longer than 10 feet developed length. With the air gap or air break below the counter, discharge to a standpipe at least 1-1/2 inches that extends at least 15 inches above the trap weir. With it above the counter, discharge through local waste piping to the sink branch tailpiece above the trap inlet, a standpipe, or the disposer's dishwasher inlet; a hose used as local waste may be no longer than 18 inches.
• Commercial: air gap or air break into a trapped and vented receptor, with indirect waste no longer than 30 inches.

Food handling establishments.

• Bar and soda fountain sinks may use indirect waste: an untrapped line needs an air gap; a trapped line may use an air gap or air break.
• Beer taps, coffee makers and soda dispenser drip pans: air break or air gap.
• Novelty boxes, ice compartments and dipper wells: air gap, indirect waste no longer than 30 inches, not combined with other equipment.
• Refrigerated rooms and cases: air gap or air break; with an air break the receptor rim is at least 2 inches below the case's strainer.
• Enclosed food equipment (urns, steam kettles, potato peelers, vending machines): air gap.
• Open culinary sinks for thawing or washing food: an independent connection through an air gap, with the fixture drain upstream of the gap no longer than 30 inches.

Other required air gaps: sterilizers and stills; vent ports of backflow devices discharging to a receptor; indoor pool deck drains to the sanitary sewer. Central vacuum units may use an air gap or air break. Outdoor pool deck drains go to the storm sewer by air gap, air break or grade, with the air break at least 6 inches below the deck.

Elevator pit drains discharge to the storm system through a sump, never by direct gravity connection. The pit-drain inlet to the sump is submerged to keep a 6-inch seal, and no sump may be in an elevator machine room.

Water treatment device waste is protected under SPS 382.41, and its tubing must meet Table 384.30-8 or 384.30-11 standards.