A clearwater sump pump discharges to an approved point such as the storm system or daylight, not the sanitary sewer in most areas. A sewage ejector serving below-grade fixtures discharges to the sanitary building drain. The sump pit must be covered and vented, and the outlet cannot flood a neighbor or the street.
What a sump pump actually does
A sump pump exists for one reason: some water sits below the level where the building drain can carry it away by gravity. When water collects in a low spot and has nowhere to fall, a pump lifts it up and out. The water gathers in a sump pit (a basin set into the floor or ground), a float switch senses the rising level, and the pump pushes the water through a discharge pipe to its release point.
The water itself comes from a few sources. Groundwater and subsoil drainage are the classic ones. This is water that seeps toward a foundation, basement, or low slab and would otherwise pool there. Foundation drains and footing drains often feed a sump for this purpose. A second case is very different. It is below-grade fixture waste, where a basement bathroom or a laundry sink sits lower than the sewer line. That waste cannot drain uphill on its own, so a pump has to lift it.
These two jobs use two different machines. A clearwater sump pump handles clean groundwater and drainage. A sewage ejector pump (sometimes called a sewage pump) handles wastewater from fixtures and is built to pass solids. Knowing which one you have is the first step to knowing where it is allowed to discharge, because the rules split sharply along that line.
The code rules: clearwater versus sewage
The governing code here is the 2024 Uniform Plumbing Code (UPC), adopted by the City of Phoenix. The UPC treats the two pump types differently, and the difference drives the legal discharge point.
For a clearwater sump carrying groundwater or subsoil drainage, the destination is an approved location. That is not automatically the sanitary sewer. Many areas ban routing clean groundwater into the sanitary system at all. They send it instead to the storm sewer or to daylight, which is an open discharge onto the ground or into a drainage channel. The reason is volume. Clean water added to a sewer that was sized only for waste can overwhelm it. The EPA names this as a cause of sewer overflows. It says overflows happen when "clean water that is improperly discharged directly to wastewater collection systems through cross connections with storm sewers and by individual homeowners through sump pumps, roof leaders or downspouts" floods the pipes during wet weather. Michigan's environmental agency puts the homeowner rule plainly. It is illegal to discharge groundwater from the sump pump to the sanitary sewer. The sewers are not built to carry the extra flow, and an overloaded sewer backs up into basements.
A sewage ejector is the opposite case. Because it pumps real waste from a below-grade fixture, it must discharge to the sanitary building drain, the same place the rest of the home's waste goes. Sending that to a storm sewer or onto the ground would be an illegal discharge of sewage.
Two physical rules apply to both. The sump pit must be covered, and it must be vented. The cover keeps debris and people out and holds back odor and gas. The vent balances air so the pump can move water and so a sewage pit does not push gas into the room. One more rule runs underneath all of this: you cannot pump what could drain by gravity. A pump is only for water that has no gravity path. Anything that can flow downhill to the building drain on its own must do so, not get pumped.
The Phoenix reality: why true sump pumps are rare here
Honesty matters more than a generic answer, and the honest Phoenix answer is that true sump pumps are uncommon in the metro area. The classic sump-pump scenario is a basement in wet ground, with a high water table pushing groundwater toward the foundation. Phoenix has very few basements, and the water table is generally deep, so the groundwater problem that drives sump pumps in the Midwest and East rarely shows up here. If a sales pitch tells you that you need a groundwater sump for a typical Phoenix slab-on-grade house, be skeptical.
What you are more likely to see locally is a sewage ejector pump. A finished space below grade, a converted lower level, or a low-lying addition can put a toilet, shower, or laundry sink below the sewer line. Those fixtures need an ejector to lift waste up to the building drain. That is a legitimate, code-covered setup. It discharges to the sanitary sewer, not to daylight.
Two other water sources get confused with sump-pump duty. Both have their own separate rules. Air conditioning condensate has its own rules for pipe size, slope, and where it may release. We cover that in our guide on air-conditioner-condensate-drain rules. Yard and area drainage is also different. It follows storm-drainage and nuisance rules, not sanitary-sewer rules. Do not assume any of these can share a sump or a discharge line. Mixing them can create an illegal connection.
Your discharge cannot create a nuisance
Where the water comes out is not just an engineering question, it is a neighbor question. A discharge point that floods someone else's yard, undermines a foundation, or runs water across a public sidewalk or street creates a nuisance, and that is its own violation regardless of which code governs the pump.
This is where the EPA's illicit discharge rules matter. Under stormwater rules, an illicit discharge is generally any flow into a storm drain system that is not made up entirely of stormwater. Say a homeowner pipes the wrong water to the wrong place, or creates pooling and runoff onto a neighbor's property. That can break both the local nuisance rules and the wider stormwater program. The EPA's guidance describes how those bad connections get found and removed. So here is the practical takeaway. A clearwater sump that daylights should release where the water can soak in or reach an approved drainage path on your own property. It should not aim a steady stream at the lot next door or the curb.
If you ever see water backing up at the lowest fixture in a home, that points to a drain or main-line problem rather than a sump issue, and our guide on a floor-drain backing up walks through what that means. The simple rule of thumb to remember: clean groundwater goes to the storm side or daylight, sewage goes to the sanitary side, nothing creates a nuisance, and you never pump what gravity could carry. When a below-grade fixture or a genuine drainage problem calls for a pump, a licensed plumber can confirm the pump type, the legal discharge point, and the cover and vent details before anything gets installed.