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This is a very basic piping schematic of what exists in most brownstones in our area.
It shows, from left to right: The pipe’s terminal to the street, the trap, the fresh air inlet from outside, a half-bathroom group in the cellar, a waste stack serving the upper floors, then another trap for the storm or leader drain from the roof of the building.

As I said, it’s very basic.

Lots of people call me after a heavy rain and want to know what they can do about the water that comes out of the drain, either through the cellar fixtures or some other outlet.

Inevitably, the homeowner mentions installing a check valve (sometimes called a backflow/backwater valve and various other names).

The place for a check valve is on the pipe just to the left of the trap.
Like this:

Having it there will keep water from the flooded city sewers from entering your building.

The only problem is, when the valve activates it closes and doesn’t allow the flow of water in either direction through the pipe.

So now that it’s raining and the pipe is closed off, where does all that water go that’s coming in from the roof (the pipe on the far right)?

The answer is….all over your floor.

There is a solution.

See it here: