4.4 Indirect Waste, Special Waste, Sumps and Sewage Ejectors
Key Takeaways
Food-handling equipment, walk-in cooler and freezer floor drains, potable clear-water waste such as sterilizers and relief valves, and swimming pool waste must discharge through an air gap (IPC 802.1.1–802.1.4).
An indirect waste air gap must be at least twice the effective opening of the indirect waste pipe (IPC 802.3.1), and indirect waste pipe longer than 30 inches measured horizontally or 54 inches total must be trapped (IPC 802.3).
A sewage pump or ejector that receives water closets must pass 2-inch spherical solids, other pumps 1/2-inch solids, and Table 712.4.2 requires 21 gpm for a 2-inch discharge, 30 gpm for 2-1/2 inches and 46 gpm for 3 inches.
Ejector discharge piping needs a check valve and, on its discharge side, a full-open valve, both accessible above the sump cover or in an access pit (IPC 712.2).
A sump pit must be at least 18 inches in diameter and 24 inches deep, with a gastight removable cover no more than 2 inches below the floor, and it must be vented (IPC 712.3.2).
Why this section matters
Indirect waste and sumps appear under Drain Waste and Vents and System Installation. Two ideas drive almost every question. First, equipment that could be contaminated by a sewer backup gets an indirect connection. Second, anything below the sewer must be pumped up with the right valves and vent.
Indirect waste (802)
An indirect waste pipe does not connect directly to the drainage system. It discharges through an air gap or air break into a trapped and vented waste receptor.
- An air gap (802.3.1) is open vertical space between the end of the indirect pipe and the receptor's flood level rim. It must be at least twice the effective opening of the indirect waste pipe.
- An air break (802.3.2) is an opening between the indirect pipe and the receptor's trap seal. The pipe may end below the receptor's rim, but it must stay above the trap seal.
Where each is required
| Equipment | Required connection | Section |
|---|---|---|
| Food storage, preparation and handling equipment (outside dwelling units) | Air gap; each well of a multi-compartment sink discharges independently to a receptor | 802.1.1 |
| Floor drains inside walk-in refrigerators and freezers in food establishments | Air gap. Where freezing is possible, the line is untrapped and discharges to a receptor outside the cold area. With a backwater valve, an air break is allowed | 802.1.2 |
| Potable clear-water waste (sterilizers, relief valves) | Air gap | 802.1.3 |
| Swimming pool wastewater, filter backwash, deck drains | Air gap | 802.1.4 |
| Nonpotable clear-water waste (process tanks, filters, drips, boilers) | Air break or air gap | 802.1.5 |
| Commercial dishwashing machines | Air gap or air break into a receptor | 802.1.6 |
| Utensil, dish and pot sinks (outside dwelling units) | Air gap or air break | 802.1.7 |
| Residential clothes washer | Air break into a standpipe or a laundry sink | 406.2 |
| Domestic dishwasher | Sink tailpiece wye, disposer inlet, or air break to a standpipe | 409.4 |
Piping and receptors
- 802.2: Indirect waste piping follows the Chapter 7 material and joint rules.
- 802.3: Indirect waste pipe more than 30 inches long measured horizontally, or more than 54 inches in total developed length, must be trapped. Waste receptors must be trapped, vented and connected to the drainage system. A receptor that takes only clear water and does not connect to a sanitary system needs no trap.
- 802.4: Every waste receptor has a removable strainer or basket, except clear-water hub drains and standpipes. Receptors may not be in concealed spaces, plenums, crawl spaces, attics, or interstitial spaces above ceilings and below floors. They need ready access.
- 802.4.1: Size each receptor for the maximum combined discharge, and install it so it does not splash or flood.
- 802.4.2: A hub drain is a hub, or a pipe extending at least 1 inch above a water-impervious floor.
- 802.4.3: A standpipe is individually trapped and rises 18 to 42 inches above its trap weir.
- 802.4.3.1: An untrapped laundry tray may drain to a washer standpipe that rises at least 30 inches above its weir and above the tray's rim, with the tray outlet no more than 30 inches horizontally from the standpipe.
- 709.4.1: A receptor taking only clear water from display cases, ice bins, coolers or freezers is rated 1/2 dfu.
Condensate and clear water
- IPC 314.2.1.1: Air-conditioning condensate may not connect directly to a DWV pipe. It may discharge into a floor sink, floor drain, trench drain, mop sink, hub drain, standpipe, utility sink or laundry sink. Condensate lines are at least 3/4 inch and slope at least 1/8 inch per foot.
- IPC 1101.3: Storm water may not drain into sewers intended for sewage only.
- IPC 1104.2: Floor drains may not connect to a storm drain.
- IPC 1111.1: Subsoil drains discharge to a trapped area drain, a sump, a dry well or an approved location above ground (section 8.2).
Special and corrosive waste (803)
- 803.1: Corrosive liquids, spent acids and other harmful chemicals may not enter the plumbing system until they are diluted, neutralized or treated in an approved dilution or neutralizing device. That device must get enough diluting water or neutralizing medium automatically. The treatment method must be approved before installation.
- 803.2 and 702.6: Chemical drainage and vent systems are completely separate from sanitary systems, built of corrosion-resistant materials (for example polypropylene, PVDF, borosilicate glass or high-silicon iron), and discharge to sanitary only after treatment.
- 901.3: Chemical waste vents are also independent. They terminate outdoors or at an air admittance valve meeting ASSE 1049.
- 1002.9: An acid-resisting brittleware trap underground must be embedded in concrete extending 6 inches beyond its bottom and sides.
- Limestone neutralizing tanks are common. The required discharge pH comes from the local sewer authority, not the IPC.
Sumps and ejectors (712)
| Rule | Requirement |
|---|---|
| 712.1 | Building subdrains that cannot reach the sewer by gravity discharge to a tightly covered and vented sump and are pumped to the gravity system. In new buildings, the sump may not receive drainage that could flow to the sewer by gravity |
| 712.2 | A check valve plus a full-open valve on the discharge side of the check valve, both accessible, located above the sump cover or, if the discharge is below grade, in an access pit with a removable cover |
| 712.3.2 | Sump pit at least 18 in diameter × 24 in deep; solid bottom; gastight removable cover no more than 2 in below the floor; vented per Chapter 9 |
| 712.3.3.1 | Discharge pipe of copper, CPVC, ductile iron, PE or PVC, rated for the pressure and temperature |
| 712.3.4 | The level control must keep effluent from rising to within 2 inches of the gravity inlet's invert |
| 712.3.5 | Connect to a building sewer, building drain, stack or horizontal branch. Into horizontal piping, use a wye into the top, at least 10 pipe diameters from the base of any stack or fixture drain |
| 712.4.2 | Pumps and ejectors receiving water closets must pass 2-inch spherical solids, others 1/2-inch solids. Grinder pumps receiving water closets need at least a 1-1/4-inch discharge opening. Macerating assemblies serving one water closet need at least 3/4 inch |
| 712.4.1 | Macerating toilet systems conform to ASME A112.3.4/CSA B45.9 |
Table 712.4.2, minimum pump capacity: 2-inch discharge = 21 gpm; 2-1/2 inches = 30 gpm; 3 inches = 46 gpm.
Sump vents (906.5)
Sewage pump and ejector sumps (other than pneumatic) are vented like a gravity system, sized by Table 906.5.1 for the pump's gpm and the vent's developed length:
| Pump discharge | 1-1/4 in vent | 1-1/2 in vent | 2 in vent |
|---|---|---|---|
| 20 gpm | 270 ft | No limit | No limit |
| 40 gpm | 72 ft | 160 ft | No limit |
| 60 gpm | 31 ft | 75 ft | 270 ft |
| 100 gpm | Less than 10 ft | 25 ft | 97 ft |
Add about 50% to the developed length for fittings if no better value is known.
- 906.5.2: A pneumatic ejector's air-relief pipe runs to an independent vent stack through the roof, and is at least 1-1/4 inches.
- 918.8: An air admittance valve may vent a sump or tank only where an engineer designed the vent system.
- 1111.1: A subsoil (groundwater) sump needs neither a gastight cover nor a vent.
Exam traps
- Food equipment: air gap. Pot sinks and commercial dishwashers: air gap or air break.
- Indirect waste air gap = 2 × the pipe's effective opening. There is no separate 1-inch minimum in 802.3.1.
- Valve order: check valve first, then the full-open valve on its discharge side.
- 21 gpm is the minimum for a 2-inch ejector discharge.
A restaurant's vegetable preparation sink drains to a floor sink. Which connection does IPC 802.1.1 require?
An air break ending below the floor sink rim but above its trap
An air break, unless the sink has three or more compartments
A direct connection through one P-trap and continuous waste
An air gap, each compartment draining separately to the receptor
What is the correct valve arrangement on a sewage ejector discharge line under IPC 712.2?
A single check valve with no isolation valve needed
A pressure relief valve installed between two gate valves
A check valve, then a full-open valve on its discharge side
A full-open valve, then a check valve downstream of it
A sewage ejector serves a basement bathroom group with a water closet and has a 2-inch discharge pipe. What does IPC 712.4.2 require?
The pump must pass 3-inch solids and deliver at least 46 gpm
The pump must pass 2-inch spherical solids and deliver at least 21 gpm
The pump must pass 1-1/4-inch solids and deliver at least 30 gpm
The pump must pass 1/2-inch solids and deliver at least 10 gpm
Sections you finish are checked off in the contents.