Stop drain backup in stacked drain line

[MOPRO]

I am the pres of an HOA board of a four story condo complex. We are looking for a device that will prevent flooding of the first floor units when there is a blockage in the drain line below the first floor. All the vertical drain lines are stacked so that the first, second, and third floors all use a common vertical main drain line. There are three condos using each common drain line. If there is a blockage in the vertical main drain blow the first floor there is an overflow in the first floor unit. Many for there units are vacation homes and unoccupied a good part of the time so overflows can go undetected for a long time. Is there a devise that will prevent the back flow and possibly alarm if there is a back flow?

[havasu]

I'd recommend a "one way" flapper valve. Several new homes in So. Cal. have them installed between the city sewer line and the houses as a way to prevent disasterous sewer muck from entering homes in the event of a clogged city sewer line.

[Reedwalker]

AKA a Backwater Valve

As a note these are not foolproof but are really the only practical line of defense.

[Plbgbear]

Yes, a backwater valve is the way to go. I've installed quite a few of them down here in Texas.