A sewage backflow preventer does exactly what the name implies: it prevents sewage from backing up and entering your basement, garage, or home.  It performs this task using some sort of valve, or a series of valves, which sense when the flow has reversed and automatically shuts down that flow until normalcy is restored.

To be on the safe side, contact a backflow expert for installation and maintenance of your backflow devices.  Backflow experts must be licensed and certified by your city and state, so do diligent research before hiring one to handle this important task.

In Texas, the name to call is City Backflow Testing for affordable backflow testing.