March 25, 2026
Sewage Ejector & Sump Pump Systems: NPC Code Guide
Plumbing Study Guide
March 25, 2026
Plumbing Study Guide
A sump or sewage ejector system is used when plumbing fixtures are located below the level of the building sewer, meaning wastewater cannot drain by gravity. Wastewater must be collected in a sump or basin and pumped up to the building drain or sewer. Typical examples include a basement bathroom below the sewer elevation, laundry fixtures on a lower level, floor drains below grade, and foundation drainage systems.
Only piping that is too low to drain by gravity may discharge into a sump or tank. Gravity drainage is always preferred — a pump system is a last resort.
Two Different Systems
Every properly designed system has five major parts: the receiving basin/sump, pump or ejector, discharge piping, vent system, and controls & safety devices.
(1) Only when gravity won't work: Do not install a pump for convenience. It is only permitted when gravity drainage is not possible.
(2) Sanitary sumps must be sealed and vented: Required to prevent sewer gas escape, prevent pressure damage, and maintain atmospheric balance.
(3) Pump or ejector required: The system must be capable of lifting sewage into the sanitary drain.
(4) Manual systems require 24-hour storage: If the system is not automatic, the basin volume must hold one full day of flow. This is a storage sizing requirement, not a pump sizing question.
(5) Building trap rule: If a building trap exists, the pump discharge must connect downstream of the trap.
(6) Required discharge order — frequently tested:
Pump → Union → Check Valve → Shut-Off Valve → Building Drain
The union allows easy servicing, the check valve prevents backflow, and the shutoff valve provides maintenance isolation.
(7) Discharge pipe sizing: Must provide optimum flow velocity at pump design flow. An undersized pipe causes friction loss and pump overload. An oversized pipe causes low velocity and solids settling.
(8) Storm sump discharge options: Either union + check valve for above-grade discharge, or union + check valve + shutoff valve.
Vent size must be one size smaller than the largest drain entering the sump, with a minimum of 2" and a maximum of 4". For macerating systems, the minimum vent size is 1½".
How to Think Like a Designer
Every pump system is sized around three questions:
Step 1 — Determine Fixture Load (NPC Table 2.4.9.3)
Add up fixture units for all fixtures in the group. Example basement group: WC = 4 FU, Lavatory = 1 FU, Shower = 2 FU, Laundry = 3 FU — Total = 10 FU. Convert fixture units to design flow using NPC 2.4.10.3, multiplying each litre per second by 31.7 to get the fixture unit total.
Step 2 — Determine Total Dynamic Head (TDH)
TDH = Static Lift + Friction Loss + Minor Losses
Static lift = 13 ft, pipe length equivalent = 50 ft, friction = 2 ft — TDH =15 ft.
Step 3 — Select Pump Using Performance Curve
The pump must deliver the required flow at the calculated TDH.
Basin size controls pump cycling frequency, pump life, odour control, and flood protection.
Example: 24" diameter basin, 30" usable depth, radius = 1 ft — Volume = 3.14 × 1² × 2.5 × 7.48 = 58 gallons.
Design Rules: Minimum pump run time of 30–60 seconds, minimum off time of 1 minute, avoid short cycling. Typical residential sewage basin working volume is 30–40 gallons.
Typical sequence from lowest to highest: OFF float → ON float (pump starts) → High-level alarm.
Given: Basement bathroom group, 12 FU total, static lift = 14 ft, horizontal run = 40 ft, 2" discharge.
When you encounter a sump question, ask: Is gravity impossible? Sanitary or storm? Is a vent required? Is the valve order correct? Is the pipe sized for velocity? How much flow is required? How high must it pump? Is the basin volume adequate?
If you understand flow, head, and storage, you can solve any sump or sewage pump question. Every design decision comes back to pressure effects, air balancing through venting, and hydraulic logic — gravity where possible, pumped only when necessary.
Situation: A basement bathroom group includes a water closet, lavatory, and shower. The fixtures are located below the building drain level, so wastewater cannot drain by gravity.
Design requirement: A sealed sewage sump with an ejector pump must be installed.
Example sizing — Typical residential sewage ejector basin:
Design considerations:
Why is a pump required? NPC code (2.4.6.3): When fixtures are below the building drain or sewer, sewage must be lifted by a sump or sewage pump.
Situation: A house has a foundation drain (weeping tile) and basement floor drain. Stormwater must discharge to grade. Gravity drainage is not possible, so a storm sump pump is required.
Example sizing:
Design considerations:
According to the National Plumbing Code of Canada, which of the following is the correct installation requirement for sewage ejectors?
Correct Answer: B — Install a sewage sump with a pump and a vented, gas-tight cover
1. Pump required when fixtures are below the sewer
NPC 2.4.6.3 – Sewage Sumps and Pumping Equipment: Where a fixture cannot drain by gravity into the building drain or building sewer, the drainage shall be discharged into a sump and pumped to the building drain or building sewer. The fixtures are below the building drain; gravity drainage is not possible, and a sewage ejector system is required.
2. Sump must be gas-tight and vented
NPC 2.4.6.3. (2): A sewage sump shall be provided with a gas-tight cover and shall be vented. Prevents sewer gas from entering the building. Required for sewage ejector pits.
3. Pump discharge must have a check valve
NPC 2.4.6.4 – Pump Discharge Piping: The discharge pipe from a pump shall be provided with a check valve and a shut-off valve. Prevents backflow into the sump. Required on ejector discharge.
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