When you flush something down the drain, you expect it to go down the pipe and not come back. One problem that can pop up in a plumbing system, however, is backflow. This can happen when there is a large change in pressure for some reason. It could be from the fire department fighting a fire and using large amounts of water, or from a burst water main. In these cases, there is a possibility that the sewer water will change direction, and instead of running down the pipes, starts travelling backwards. If this happens, you could end up with water coming back up into your house, or having contaminated drinking water, with the serious health side effects that can bring.
To prevent this from happening, an atmospheric vacuum breaker is used. These devices will usually be installed about a foot above ground on a pipe that goes in a square shape. This is a cheap way of ensuring that backflow doesn’t happen to you.
