Once you have installed the faucet and taps, one of the last things you need to do when installing or refurbishing a sink is to fit the sink drain. The metal (sometimes PVC) part of the drain visible in the bottom of your sink is connected to a straight piece of pipe beneath the sink called the tail piece. Connected to the tail piece is a curved piece of plumbing called the P-trap, which traps water in its curved section, preventing sewer gases from escaping through the sink and into your home. Fitting a sink drain involves hooking up all these components and, although it may sound complicated, is actually quite simple and is the perfect project for a first time plumber.
Clean out the bottom of the sink, paying special attention to the hole where the drain will be installed. Use a standard bathroom cleaner and rags.This will help ensure a proper seal.
Turn the sink flange over so the bottom is facing upwards. Roll out a thin bead of plumber's putty. Press this into place around the perimeter of the underside of the flange. Turn it back over so it is right side up. Press it into place in the drain receptacle in the sink, twisting slightly as you do so to distribute the putty. Hold the drain with one hand or, if this is a large countertop/sink, have an assistant hold the flange in place for you.
Position yourself underneath the sink. Insert the straight tailpiece into the underside of the sink flange. Tighten the tailpiece nut against the flange.
Slip the rubber washer and large plastic jamb nut over the end of the tailpiece until they are flush with the bottom of the sink. Tighten the jamb nut with the pliers.
Wrap the threads on the bottom of the tail piece and the sewer inlet with plumber's tape. Trim off any excess.
Slip the P-trap into position between the end of the tail piece and the sewer inlet. Tighten the couplings hand tight.
If this is a metal sink drain installation (as opposed to PVC), you can further tighten the couplings in Step 6 with a pair of pliers. It's possible to use silicone caulk in Step 2 as opposed to plumber's putty.