Indirect Waste, Wet-Vented & Special Wastes
Some waste must never connect directly to the drainage system. Chapter 8 governs indirect waste — discharge that reaches the drain only after passing through an air gap or air break so that sewage can never back up into food, sterile, or potable-adjacent equipment. It also covers air-conditioning condensate, clothes-washer standpipes, waste receptors, swimming-pool and refrigeration drainage, and corrosive special/chemical wastes that need pre-treatment or special materials.
Where Indirect Waste Is Required
Equipment that must discharge through an air gap or air break
An indirect waste connection (through an air gap or air break to a receptor) is required wherever a direct connection could allow drainage to contaminate food, sterile items, or potable water. Typical examples:
Refrigerators, ice machines, food-prep sinks, steam tables, dishwashers, bar sinks.
Sterilisers, autoclaves, and similar equipment in clinics and hospitals.
Cooling coils, condensate, overflow pans, and equipment drains.
Drinking fountains, water-station drains, and similar fixtures.
Air Gap vs Air Break
Two ways to break the connection — know the difference
An unobstructed vertical space between the waste outlet and the flood-level rim of the receptor — not less than 25 mm (§801.3). No physical contact. Highest protection.
The indirect pipe ends below the flood rim but above the trap-seal water of the receptor — it may touch the side but cannot submerge. Used where an air gap is impractical and back-siphonage risk is low.
The receptor itself must be trapped and vented, accessible, and sized to take the discharge without overflowing. The indirect line should be as short as practical and may need its own trap when it exceeds the allowed developed length.
The air-gap principle. The indirect waste outlet discharges into the open, above the flood-level rim of the receptor, with an unobstructed vertical gap of not less than 25 mm (§801.3). A submerged outlet has no air gap and could allow backflow — exactly what an indirect connection must prevent.
Indirect-Waste Air Gap Requirement
Per §801.3, the air gap between an indirect waste outlet and the flood-level rim of its receptor shall not be less than 25 mm.
Food-Handling & Sterile Equipment
Commercial kitchens, restaurants, and health-care facilities
Equipment in which food, drink, or sterile goods are stored, prepared, or handled discharges to the drainage system only through an air gap into a floor sink or standpipe receptor:
- Commercial dishwashers and pot/pan sinks via an air-gap to a floor sink;
- Walk-in coolers, reach-in refrigerators, and ice machines via condensate/clear-water lines to a receptor;
- Steam kettles, steam tables, and food-prep sinks indirectly connected;
- Hospital sterilisers and autoclaves indirectly connected with the proper receptor.
Air-Conditioning Condensate
Clear-water waste that must be indirectly drained
Condensate from air-conditioning and refrigeration coils is clear-water waste and shall be disposed of by indirect waste — never connected directly to a sanitary drain or vent.
- Route condensate to an approved receptor (floor drain/sink) with an air gap, or to an approved exterior point;
- Provide a secondary (overflow) drain or drip pan for concealed equipment so a blocked primary line cannot damage the building;
- Size the condensate line for the equipment capacity and slope it to drain.
Clothes-Washer Standpipe
The receptor for an automatic washing machine discharge
An automatic clothes washer discharges (indirectly) into a trapped, vented standpipe. Typical requirements:
Per §804.1, the standpipe shall extend not less than 0.45 m nor more than 0.8 m above its trap, and shall be roughed-in not less than 15 cm nor more than 45 cm above the floor.
The standpipe has its own trap and is vented like any fixture drain.
The washer hose discharges into the open standpipe — an air break, not a sealed connection.
Standpipe sized for the washer discharge (commonly 50 mm) to avoid overflow.
Waste Receptors
Where the indirect waste actually lands
A receptor receives the indirect discharge and conveys it to the drainage system. Receptors (floor sinks, funnels, hub drains) shall be:
- Accessible — never installed in a concealed or inaccessible space such as a closed wall or under a fixed cabinet without access;
- Trapped and vented, with a removable strainer;
- Shaped and sized so discharge does not splash beyond the receptor;
- Located to be readily cleaned and inspected.
Swimming Pool & Refrigeration Wastes
High-volume clear-water and equipment drainage
Drainage from swimming pools, fountains, cooling towers, and refrigeration equipment is handled as indirect waste so it cannot cross-contaminate the sanitary system:
- Pool deck drains, gutter drains, and filter backwash discharge indirectly to an approved point;
- Pool/fountain drains are never directly connected to the building drainage system;
- Cooling-tower and refrigeration blowdown reaches the drain through an air gap.
Special & Chemical Wastes
Corrosive, acid, and other non-domestic wastes
Wastes that are corrosive, acidic, flammable, or otherwise harmful to the piping, the public sewer, or the treatment process shall not enter the drainage system until they are rendered safe:
Neutralise, dilute, or treat the waste (e.g. acid-neutralising tanks for laboratories) before discharge.
Use chemical-resistant piping and fittings on the special-waste system — ordinary drainage pipe may not survive.
Special wastes are kept on a separate, identified piping system until safe to combine.
Discharge limits are set by the sewerage authority and the Building Official.