Even if you have never had any trouble with your plumbing, you may eventually have issues with the main drain in your home. Once a main drain becomes clogged, water can back up through the bottom-level toilet connected to the drain.
All of the out-flow pipes in a home typically feed into the main drain, which exits the house and leads into the city sewer line. Thus, the contents of an upstairs toilet will flow into the main drain line of the home when the toilet is flushed.
