Basics on Pipes Under the Kitchen Sink

Kitchen sink pipes must be a certain size to ensure they can efficiently accommodate the drainage load they are required to transport. Certain types of pipe and standard features underneath the sink are found on all kitchen sinks. All of the pipes and fittings must be properly installed to avoid any leaks.

Drain Pipe Size

Kitchen drain pipes have a minimum size of 1 1/2 inches but are sometimes installed with pipe sizes of 2 inches. This size is the diameter of the pipe. The size of the drain pipes for kitchen sinks, and all fixtures inside a house, are governed by local or state plumbing codes. These codes are normally adapted from the plumbing codes developed by either the Uniform Plumbing Code or the International Plumbing Code, which sets the standards for healthy, safe plumbing.

The Trap

A kitchen sink will use either a P-trap or an S-trap. The trap is the curved piece of pipe that you see underneath the sink before the pipe goes either into the wall underneath the sink or into the floor. Basically, P-traps are used in modern homes and are used when the pipe that the trap connects to is horizontal and extends through the back wall underneath the sink. The S-trap is used when the pipe extends down vertically through the floor. The traps are named "P" or "S" to denote their shapes.

Connection to Sink

A tailpiece connects to the sink basket with a locknut. In a double-sink, an elbow at the bottom of the tailpiece, often under the left basin, connects the basin to the drain pipe of the other sink basin via a T fitting. This fitting leads down to either a P-trap, which connects to the pipe going through the wall, or an S-trap, connected to the vertical pipe going through the floor.

Pipe Composition

Kitchen sink pipes can be made from different types of materials. Modern kitchen pipes are usually made from white PVC pipes. The kitchen sink pipes in older homes were made of copper, which was found to deteriorate over time. In the past, the pipes were also sometimes made of galvanized steel or cast iron. PVC is also preferred because of the ease of installation it offers as well as the ease with which it can be taken apart for clearing clogs or changing out.