Why You Shouldn’t Connect Your Sump Pump to the Sewer

Discharging your sump pump into the city’s sanitary sewer system is bad news. While this might seem like an easier and more attractive option than running a discharge tube from the sump pump to the exterior, it’s illegal in most cities here in Minnesota when the home is connected to the city sewer.

What it looks like

In layman’s terms, you can’t connect your sump pump discharge to the same place where you flush your toilets. That’s called the sanitary sewer system. When this happens, it’ll look something like this:

Sump pump discharge to santary sewer explained

This is pretty obvious and blatant, but sometimes it’s more subtle. The photo below shows a corrugated drain line running from the sump pump to the floor drain. Where does the floor drain go? To the sanitary sewer, of course.

Sump pump discharge into floor drain explained

Finally, one more version of this is a very shallow sump pit with a floor drain at the bottom of it. The black corrugated tubing coming into the sides of the pit is drain tile, and the floor drain at the bottom drains to the sanitary sewer.  In Minneapolis, this is a required repair item for their Truth-In-Sale of Housing program.

Drain tile floor drain

But it’s not always this obvious. Sometimes, we just find a hole in the basement floor with a floor drain at the bottom. This is the same thing, just without drain tile.

Square sump basket with a floor drain

Why does this matter?

Cities don’t allow this because you’re basically dumping rainwater into the sanitary sewer system. Cities have completely separate drain systems for rainwater, called storm sewers. Those things take rainwater directly to our rivers and lakes. When we dump rainwater into sanitary sewers, we overload the sewage treatment facilities, which can cause two big problems:

  1. Untreated sewage is forced into our rivers and lakes. Yuck.
  2. Sewage backs up into people’s homes. Double yuck.

The City of Golden Valley has some excellent explanations of all of this at their website, explaining how this costs hundreds of millions of dollars each year. This is such a serious issue that many cities throughout the metro area have been forced to conduct inflow and infiltration (I/I) inspections. Not only do they look for illegal sump pump connections, but they also scope the sewer line to make sure rainwater can’t find its way in there through failed joints and cracks.

Additionally, sump pumps shouldn’t discharge to the sanitary sewer because municipal water departments bill homeowners for their sewer usage based on their water usage. When a sump pump discharges into the sanitary sewer, the city has no way of tracking and billing for this additional usage of the sewer. When a homeowner discharges their sump pump into the sanitary sewer, they’re getting a service for free that everyone else has to pay for

If you have this type of setup at your own home, the ‘good citizen’ thing to do is to make the sump pump discharge to the exterior. In some cities, they’ll even let you connect your sump pump discharge directly to the storm sewer system, which makes for a very solid, inconspicuous installation.

Sump pump to storm sewer
Written By

Reuben is a second-generation home inspector with a passion for his work. He grew up remodeling homes and learning about carpentry since he was old enough to hold a hammer. Reuben grew up thinking he was going to be a school teacher because he enjoyed teaching others so much. In a sense, that’s a lot of what home inspections are about, so Reuben truly does what he loves. Sharlene has worked with Structure Tech since 2000 and Reuben has been contributing to her blog since 2008.

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