A sump pump moves clear water, like groundwater or storm runoff, and the plumbing code says it handles drainage except raw sewage. An ejector pump lifts sewage from low fixtures inside one building. A lift station does the same job for a whole site or sewer system, with a wet well, two pumps and alarms.
Sump pump: clear water only
The 2024 International Plumbing Code (IPC) defines a sump pump as "an automatic water pump powered by an electric motor for the removal of drainage, except raw sewage, from a sump, pit or low point." The key words are "except raw sewage."
You'll find sump pumps in elevator pits, below-grade parking, subsoil drains around a foundation and low areas that collect storm water. Under IPC Section 1113, the storm-side pit must be at least 18 inches across and 24 inches deep, with a removable cover strong enough for its location, and the discharge line needs a gate valve and a full-flow check valve. Subsoil sumps don't need a gastight cover or a vent, because there's no sewer gas in clear water. The storm chapter uses the same pit rules for storm drains that sit too low to leave by gravity: IPC 1112 sends building subdrains below the public sewer level to a sump or receiving tank whose contents are lifted automatically.
Where that water can go is its own set of rules. Our page on where a sump pump can legally discharge covers it. The short answer is the storm system or an approved spot outside, not the sanitary sewer in most places.
Ejector pump: sewage from one building
When restrooms, sinks or floor drains sit below the building's sewer line, their waste goes to a sealed pit and a pump lifts it up to the gravity drain. In the trade that's an ejector pump or sewage ejector. The IPC's formal term is sewage pump, and it reserves "sewage ejector" for an older design that lifts sewage with a high-velocity jet of steam, air or water. Most units sold as "ejector pumps" today are submersible sewage pumps.
The code treats this pit very differently from a sump. Under IPC Section 712:
- The pit must have a gastight removable cover and be vented, because it holds sewage.
- A pump that takes toilet waste must pass solids up to 2 inches. Grinder pumps, which chop solids first, may use a smaller discharge opening of at least 1 1/4 inches.
- The discharge line needs a check valve and a full-open valve, reachable for service.
- In new buildings, only drains that can't reach the sewer by gravity may go to the pit.
The vent is sized by the pump's discharge rate under IPC 906.5. That's why an ejector pit has two pipes coming out of the lid, a discharge and a vent, while a sump often has just one.
### Where grinder pumps and macerating toilets fit
Both are types of sewage pump. A grinder pump chops solids before pushing them out, which is why the IPC lets a grinder that takes toilet waste use a discharge opening as small as 1 1/4 inches instead of passing 2-inch solids. A macerating toilet is a toilet with its own small pump behind it, often used where there's no floor drain to tie into. IPC 712.4.1 says those systems must meet the joint ASME and CSA standard for macerating toilets and be installed per the manufacturer's instructions. Under an exception in IPC 712.4.2, one serving a single toilet can have a discharge as small as 3/4 inch.
Our page on whether a building needs a sewage ejector or lift station walks through when a commercial building needs one.
Lift station: sewage from a whole site
A lift station does the ejector's job at a bigger scale. It collects sewage from many fixtures, buildings or homes in a wet well and pumps it through a pressurized pipe called a force main to a higher gravity sewer. Cities run large ones in the public system, and developers build private ones for shopping centers, office parks, apartment complexes and subdivisions that can't reach the public sewer by gravity.
In Arizona, a site lift station usually falls under ADEQ's sewage collection system rule, A.A.C. R18-9-E301. That rule requires, among other things, at least two pumps, the ability to run at design flow with one pump out of service, high and low level alarms at the site and at a control center, and standby power for stations averaging more than 10,000 gallons a day. See does a private lift station need ADEQ approval for the permit side.
### How a lift station's wet well is sized
The state rule sets the numbers. The minimum wet well volume in gallons is one quarter of the minimum pump cycle time in minutes times the total pump capacity in gallons per minute. Sewage shouldn't sit longer than 30 minutes unless it's aerated, chemically treated or the well is well ventilated, because stale sewage makes hydrogen sulfide. A wet well built for more than 5,000 gallons a day needs at least 20 square feet of floor area, and the pumps must pass a 2.5-inch sphere or be grinders. That's a bigger solids target than the 2 inches the plumbing code sets for a building pump.
Side by side
| Sump pump | Ejector (sewage) pump | Lift station | |
|---|---|---|---|
| Handles | Clear water, no raw sewage | Sewage from low fixtures | Sewage from a site or system |
| Serves | A pit, low area or subsoil drain | One building | Many fixtures, buildings or homes |
| Pit cover | Removable; subsoil sumps need no gastight cover | Gastight, removable | Secured wet well or vault |
| Vent | Not for subsoil sumps | Required | Designed ventilation and odor control |
| Main rules | IPC 1113 and local discharge rules | IPC 712 and the city plumbing permit | ADEQ 4.01 rule plus city standards |
| Typical pumps | One | One or two | Two or more |
Why the difference matters
Mixing them up causes trouble in both directions. A sump pump dropped into a sewage pit will clog on solids it wasn't built to pass. The sewage pump has to pass 2-inch solids for toilet waste; the code sets no solids rating for a clear-water sump pump. Storm water piped into a sewage ejector or the sanitary sewer breaks IPC 1101.3, which says storm water "shall not be drained into sewers intended for sewage only." And a sealed ejector pit treated like a sump, lid cracked open or vent capped, lets sewer gas into the building.
If you're not sure what's in your floor, look at the lid and pipes before you open anything. Bolted or sealed lid, two pipes and a vent going up means sewage. Loose lid and one pipe usually means clear water. A buried vault outside with a control panel and alarm light means a lift station, and our page on sewage lift station basics explains how it works.
For a Phoenix area building, slow drains or backups upstream of any of these are ordinary drain work. HQ Plumbing and Air can camera and clear the lines 24/7, with the price given up front before work starts.