Regardless of what particular type of bathroom sink you have, from a vessel sink to a vanity sink, the plumbing for the drain is normally connected in the same way, and is made up of the same components that serve the same functions. When you understand the different components involved, you can better understand how to properly install the sink drain plumbing.
The flange is the ring that is installed directly on top of the sink's drain opening. To insert it, you apply a bead of plumber's putty around the rim of the drain hole, or apply a suitable sealant around the rim on the underside of the flange, and press the flange down into place atop the sink's drain hole. The flange is often made of either chrome or brass, although some are now made of plastic.
Tailpiece & Stopper Assembly
The tailpiece is the portion of pipe directly underneath the sink, attached to the bottom of the drain flange. The bottom of the tailpiece attaches to the top of the sink's p-trap below it. The assembly to the pop-up stopper inside the sink drain connects inside this tailpiece. The pop-up assembly's pivot rod is the horizontal rod that enters through the back of the tailpiece, connecting with the bottom of the pop-up stopper inside the tailpiece. The pivot rod connects to one of the holes in the vertical clevis, to which the faucet's lift rod is attached in order to lower and raise the stopper.
When you look underneath the sink, you can identify the p-trap as the curved pipe that runs down, then curves back upwards. The bottom of the tailpiece inserts into the top of this trap. Check your local building codes to make certain what size this trap should be, but standard codes usually always set the diameter of the trap and the other bathroom sink pipes at 1 1/4 inches. Each end of the trap is secured by slip nuts, which can simply be loosened and slipped off the trap so that the trap can be removed when needed. The trap functions as a blocking mechanism to seal out sewer gases from rising up through the sink drain, by keeping an amount of water stored within the trap's curved area.
Drain Arm and Stub-Out
The drain arm is the horizontal pipe that runs from the end of the p-trap into the wall underneath the sink. Slip nuts provide the connection between this pipe, and the p-trap and wall stub-out. The stub-out is the short piece of pipe that protrudes from the wall, providing the route by which the sink water travels. It is generally installed about 15 to 17 inches above the floor and is often surrounded by an escutcheon plate.
The pipes for the bathroom sink's drain plumbing are normally made of either plastic or metal. More installations are choosing the white PVC pipes over metal because of the ease of installation and removal that PVC pipes allow. As far as appearances go, PVC pipes usually complement a white sink better.