A client’s house down by the Gowanus Canal was being flooded every time there was a major storm, when a large rain came, the toilets overflowed. Not Fun. This was happening because the storm drains in NYC connect to the sewer mains, and down by the canal you get all the water that is draining down from Park Slope. That large amount of water has to go somewhere, and it backs up into the plumbing in the houses along the canal.
Installing a backflow preventer in the main sewer pipe in the basement prevents the water in the city main from backing up into the house line.

