A kitchen sink drain is sized to meet the usage of the kitchen sink. Certain size pipes allow for a certain flow rate, which is actually measured using mathematical equations and scientific theories. If installing your own drain, use correctly sized pipes to prevent clogs and provide proper drainage flow.
Typical Kitchen Drainpipe Size
The drainpipe for the kitchen sink is at least 1 1/2 inches in diameter, which is the standard size for kitchen sink drains, and it provides enough drainage room for all your kitchen activities like dishwashing, cooking and food waste disposal. This size pipe is common at hardware stores and plumbing supply stores, so it is easy to procure and is considered the standard for kitchen sink drains.
Using Smaller Drains
Some kitchen drains use smaller, 1 1/4 inch pipes without problems. However, for the kitchen, using the 1 1/2-inch pipe is wise. Smaller drainpipes have a tendency to clog more frequently due to their smaller diameter. Scraps of food and waste will plug up a smaller drain if they lodge inside the pipe and stick to the walls. The 1 1/4-inch pipe is used for bathroom sink drains, which have a 1 1/4-inch drain size. The bathroom drain handles less food and waste than a kitchen drain, so a smaller pipe is required.
Installing the Drain
The drainpipe, called a tail piece, fastens onto the end of the drain assembly -- the round piece installed in the base of the sink -- with a slip nut, a threaded nut on the end of the pipe. The pipe connects to the sink basket, the portion of the sink drain visible below the sink basin. This sink basket is threaded and coated with PVC cement before installing the drainpipe. The sink basket is sized to match a 1 1/2-inch drainpipe. All you need to do is screw the drainpipe onto the sink basket, and connect the 1 1/2-inch P-trap to the drain.
Connections to the Main Drain
The main drain line in newer homes today runs straight back into the wall. This horizontal pipe connects directly to the end of the P-trap to complete the drain assembly. The pipe is usually 1 1/2 inches to 2 inches in diameter. If the pipe is larger than the P-trap pipe, install a reducing bushing with 2- and 1 1/2-inch diameter ends on the drain line to connect the two different sized pipes. Normally, this is the only reducing bushing needed when installing a kitchen drain.