Well the original sump pump is plumbed into the city drain, so I did the same with the backup pump.I live in an are with a high water table so my sump pump is the most important appliance in my house. I have a battery backup and a generator. I also have a spare pump ready to go if needed.
A couple of things go along with water backup pumps. First, do your local codes allow you to pump sump water into the sewer system. Mine does not because it could overload the system's capacity and back up sewage into other people's homes. Second, if you are allowed to connect you need to prevent cross contamination between your potable water supply and the sewer. Normally that requires an air gap between the two systems. Otherwise you must discharge the pump outdoors.
Eric
I have been keeping an eye on the sump level from time to time and very little water actually makes its way into the pit, I would estimate a few gallons a day, so the pump runs perhaps 10-30s, once or twice a day. So were definitely not going to overwhelm the system. The reverse flow valve should prevent cross contamination and the actual supply is controlled by a manual valve and will be off unless the power fails.
I think we're good to go.