You probably shouldn’t connect it to the sanitary sewer line but many sump pumps are connected to storm sewers, and that’s generally OK. It might seem like the most convenient option to discharge your pump into the sanitary sewer, but you’re actually risking water and sewage damage to your home. While it may not be illegal in your area, connecting your sump pump to the sanitary sewer is in fact illegal in much of the U.S.—and for good reason.
During big storms or heavy rainfall, the sewage treatment plants can become overloaded. What does that mean for you? Nothing, if you’re not connected to the sewer line. If you are, it can mean sewage backing up through the line and overflowing into your home. Also, cross-connecting your sump pump to the sanitary sewer system can overload the sewers if too many sump pumps are connected.
The other big reason not to connect your sump pump to the sanitary sewer line is because when it is connected, the city is unable to track your water usage. Municipal departments track each home’s use individually, which can’t be done with accuracy if you’re connected to the sewer line. Basically, this equates to stealing from your city’s water department.
>Before working with your sump pump and the sewer line, make sure to talk to the local municipal water department or the local plumbing board about your sump pump discharge options. However, more than likely the right thing to do, as well as the smart thing to do, is to connect your pump to the exterior of your house to prevent sump pump overflow.