1. The S Pipe

Why are some pipes under sinks shaped like the letter S?

Author: Dr. George Mathew, Illustrator: RE Chamblee, Editors: Ellen Curtin, Dr. Keith Mac Adam, Dr. Mark Manley, Julia Bedell, Dr. Joy Joseph, Dr. Joseph Straley, Tom Vdaketh, Lori M Barrett

Suppose your sink drained into a straight pipe, so the waste fell straight down to the sewer pipe. If some of the waste got stuck to the side, it would smell after a few days. Nothing would stop that stinking smell from coming back up into your rooms (and into your nose).

To prevent rotten smells from getting into your rooms, engineers and plumbers use the S pipe. At all times, there is some water in the bend to keep the unwanted gases away. Water can't drain away from the low part of the bend without flowing uphill! The S pipe is called a trap because the water it holds traps smelly gases and keeps them from coming out of the pipes.