7.2 Sumps, Sewage Ejectors, Grinder Pumps, & Macerating Systems (UPC 710)

When a Sump Is Required

Section 709.1 prefers gravity drainage wherever practicable. When fixtures are below the crown level of the main sewer, 710.2 requires them to drain by gravity into an approved watertight sump or receiving tank. From there the waste is lifted into the building drain or sewer by an approved ejector, pump, or equivalent mechanical device.

Section 710.7 requires the drainage and vent piping serving sumps and lifting devices to follow the same rules as gravity systems. That includes trapping, venting, sizing, and cleanouts (707.11 addresses cleanouts for pressure drainage).

Sewage Ejectors and Pumps Receiving Water Closets or Urinals (UPC 710.3)

Discharge Line (UPC 710.4)

1. Use approved pressure-rated material.
2. Provide an accessible backwater or swing check valve and a gate or ball valve. The gate or ball valve goes on the discharge side of the check valve, so the check can be isolated and serviced.
3. Where the discharge connects to a horizontal gravity drain, it must enter from the top through a wye branch.
4. 710.5: The building drain or sewer receiving pump discharge is sized at 2 DFU per gpm of flow. A 30 gpm ejector therefore adds 60 DFU to the drain it discharges into.

Sump and Receiving Tank Construction (710.8)

• Watertight, made of concrete, metal, or other approved material. Poured concrete must be reinforced and designed to recognized standards. Metal must be thick enough for its purpose and protected against corrosion inside and out.

Controls and Alarms (UPC 710.9)

• Sumps and receiving tanks discharge automatically.
• In a public use occupancy: dual pumps or ejectors that alternate in normal use and operate independently in case of overload or failure.
• An audio and visual alarm, readily accessible, signals pump failure or overload.
• The lowest inlet must be at least 2 inches above the high-water or "starting" level of the sump.

Covers and Vents (UPC 710.10)

• Covers must be substantial, with a bolt-and-gasket manhole or equivalent opening for inspection, repair, and cleaning.
• The vent comes off the top and extends separately through the roof or, where permitted, combines with other vents.
• The vent must keep the sump at atmospheric pressure. It may not be smaller than Table 703.2 requires for the fixtures discharging into the sump, and never less than 1-1/2 inches.
• Once the sump vent combines with the vents of the fixtures discharging into it, the combined vent need not exceed the size required for all those fixtures.
• A vent from an air-operated sewage ejector may not combine with other vents.

Other Lifting Devices

• Air tanks (710.11): Equal in cubic capacity to the ejectors they serve, with air pressure of at least 2 pounds per foot of height the sewage is raised. Water-operated ejectors are prohibited.
• Grinder pumps (710.12) are permitted. Their discharge piping is sized per the manufacturer's instructions but is at least 1-1/4 inches, with a check valve and fullway shutoff valve in the discharge line.
• Macerating toilet systems and pumped waste systems (710.13) may replace a sewage pump system where approved by the AHJ. They must comply with ASME A112.3.4/CSA B45.9 and be installed per the manufacturer's instructions:
  • The sump is watertight and gastight.
  • Discharge piping is sized per the manufacturer's instructions, but at least 3/4 inch, with a check valve and fullway shutoff valve in the line or inside the unit.
  • Fixtures discharging into the macerator are vented per the code, and the sump is vented per the manufacturer's instructions. That vent may connect to the fixture venting.

Access to Mechanical Devices (UPC 710.6)

Backwater valves, gate and ball valves, unions, motors, compressors, air tanks, and other devices required by 710 must be accessible for inspection and repair. Unless continuously exposed, they go in a masonry pit with an adequately sized removable cover.

Worked Scenario: Basement Bathroom in a House

A basement bathroom (water closet, lavatory, shower) sits below the sewer crown.

1. Sump: watertight, with a gasketed, bolted cover.
2. Ejector: single-dwelling pump rated for at least 20 gpm that passes a 1-1/2-inch solid.
3. Discharge: 2-inch pressure-rated pipe, with a check valve and then a gate or ball valve downstream of it. It enters the horizontal building drain from the top through a wye.
4. Venting: the fixtures are vented as in a gravity system. The sump vent is at least 1-1/2 inches and may combine with the fixture vents.
5. Drain sizing: add 2 DFU per gpm of pump discharge to the drain that receives it.
6. Upper floors: they stay on gravity drainage. Any gravity-drained fixtures on a floor below the next upstream manhole cover still need a backwater valve (710.1; Section 6.4).