know your plumbing system

Outgoing: Where Does It All Go?
When wastewater goes down the drain, it first passes through a "trap," a U-shaped curve in the pipe that retains a small amount of water so that sewer gas, which is very dangerous to breathe, cannot flow up through the pipes and enter your home. Then it passes into the main waste drainpipes. The main component of the waste drain is the "soil stack," a vertical "stack" of pipes that is connected to the outbound sewer line.

The stack has a vent that extends vertically out through the roof, allowing gases to escape and promoting drain flow by drawing air inward. It is very important to keep this vent clear, as plugged vents can trap dangerous gases and inhibit drainage. Most newer waste systems use rigid plastic PVC (polyvinyl chloride) or ABS (acrylonitrile butadiene styrene) pipes that are sealed with glue. Older homes generally have had cast iron pipe sealed with lead solder, although some new homes also use cast iron sealed with neoprene in order to avoid the noise plastic creates when water is draining through it.