10.3 Sumps, Sewage Ejectors, and Macerating Toilet Systems

Sumps versus subdrains

Two related sections, easy to mix up:

• IPC 712 Sumps and Ejectors — the sanitary side. Sewage and waste that cannot reach the sewer by gravity.
• IPC 1113 Sumps and Pumping Systems — the storm side. Clear water, subsoil drainage and building subdrains.

They share dimensions but not requirements. The storm sump pit (1113.1.2) also requires 18 inches in diameter and 24 inches in depth, but its cover need not be gastight and "the subsoil sump shall not be required to have either a gastight cover or a vent" (1111.1). The sanitary sump must be gastight and vented, because it contains sewage.

The sump pit — IPC 712.3.2

All three of "unless otherwise approved," "gastight" and "vented per Chapter 9" appear in exam distractors. The vent is not optional: a pumped sump displaces its entire volume of air on every cycle, and without a vent that air would blow through the nearest trap seal.

Valves — IPC 712.2

A check valve and a full open valve located on the discharge side of the check valve shall be installed in the pump or ejector discharge piping between the pump or ejector and the gravity drainage system. Access shall be provided to such valves.

Order matters and is tested: pump, then check valve, then full open valve. The check valve stops the discharge column from draining back into the pit; the full open valve downstream of it lets you isolate and service the check valve without draining the line.

Location: the valves shall be located above the sump cover required by 712.1; or, where the discharge pipe from the ejector is below grade, accessibly located outside the sump below grade in an access pit with a removable access cover.

Discharge piping — IPC 712.3.3

• Materials (712.3.3.1): copper or copper-alloy, CPVC, ductile iron, PE, or PVC.
• Ratings (712.3.3.2): rated for the maximum system operating pressure and temperature; fitting materials compatible with the pipe; suitable for burial where buried.

Connection to the drainage system — IPC 712.3.5

Pumps connected to the drainage system shall connect to a building sewer, building drain, soil stack, waste stack or horizontal branch drain. Where the discharge line connects into horizontal drainage piping, the connection shall be made through a wye fitting into the top of the drainage piping, and such wye fitting shall be located not less than 10 pipe diameters from the base of any soil stack, waste stack or fixture drain.

Three constraints in one sentence: wye fitting, into the top, and 10 pipe diameters clear of any stack base or fixture drain. Compare IPC 704.3, which imposes the same 10-diameter clearance on ordinary horizontal branches connecting at a stack base.

Effluent level — IPC 712.3.4

The effluent level control shall be adjusted and maintained to at all times prevent the effluent in the sump from rising to within 2 inches of the invert of the gravity drain inlet into the sump.

If sewage backs up into the inlet, the gravity line upstream floods and the fixture it serves stops draining.

Pump capacity and solids handling — IPC 712.4

712.4: a sewage pump or sewage ejector shall automatically discharge the contents of the sump to the building drainage system.

712.4.2 Capacity:

• Pumps or ejectors that receive the discharge of water closets shall be capable of handling spherical solids up to and including 2 inches in diameter.
• Other pumps or ejectors shall handle spherical solids up to and including 1/2 inch.

Two exceptions to the solids rule:

1. Grinder pumps or grinder ejectors receiving water closet discharge shall have a discharge opening of not less than 1-1/4 inches.
2. Macerating toilet assemblies serving single water closets shall have a discharge opening of not less than 3/4 inch.

The logic: a grinder or macerator reduces solids before pumping, so it does not need a 2-inch passage. A conventional sewage ejector passes solids whole and does.

712.4.1 Macerating toilet systems: comply with ASME A112.3.4/CSA B45.9 and are installed in accordance with the manufacturer's instructions. The same standard governs fixtures with a pumped waste under IPC 405.5.

Worked design: a basement bathroom below the sewer

A finished basement bathroom has a water closet (3 dfu private 1.6 gpf), a lavatory (1 dfu) and a shower at 2.5 gpm (2 dfu). The building drain is above the basement floor, so gravity discharge is impossible.

Step 1 — sump required. IPC 712.1: a tightly covered and vented sump with automatic pumping equipment. In new construction, no gravity-capable piping may be routed to this sump.

Step 2 — pit. Not less than 18 inches in diameter, not less than 24 inches deep, solid bottom supporting the pump, gastight removable cover not more than 2 inches below floor level, vented per Chapter 9, access provided (712.3.2).

Step 3 — pump selection. The pump receives a water closet, so it must pass 2-inch spherical solids (712.4.2) — unless a grinder pump is chosen, which may have a 1-1/4-inch discharge opening.

Step 4 — discharge size and capacity. Choosing a conventional ejector with a 2-inch discharge, Table 712.4.2 requires a minimum capacity of 21 gpm.

Step 5 — valves. In order from the pump: check valve, then full open valve on the discharge side of the check valve, both with access, located above the sump cover (712.2).

Step 6 — discharge connection. Into the top of the horizontal building drain through a wye fitting, located not less than 10 pipe diameters from the base of any stack or fixture drain. For a 4-inch building drain that is 40 inches (712.3.5).

Step 7 — level control. Set so effluent never rises to within 2 inches of the invert of the gravity inlet (712.3.4).

Step 8 — vent. The sump vent is sized and installed per Chapter 9; see Chapter 12 of this guide for individual vent sizing under IPC 911 and 906.