A normal sink drain assembly begins in the drain opening and ends in the stub-out in the wall behind the sink or the floor under it. The assembly includes the strainer, tailpiece and pop-up stopper — which frequently arrive together with the faucet to form a matching group — and also the P-trap, which you purchase separately. When you buy a new faucet and drain assembly, it is normally a fantastic time to replace the trap. The older one is probably stained or discolored, and new ones are cheap. Things may get messy, so have some rags handy.
Disconnect the P-trap from the drain stub-out along with the tailpiece, which is the pipe which goes downward from the sink. Loosen the compression nut at each joint by turning it counterclockwise. Pull the combined apart. Keep the trap erect until you can safely dump the water out.
Squeeze the clamp on the end of the lever arm for the pop-up stopper and pull the plate which connects the lever to the lift pole. Unscrew the nut holding the lever to the tailpiece and pull on out the lever.
Unscrew the nut holding the strainer to the sink, using adjustable pliers. Hold the tailpiece with a single hand while you turn the nut to maintain the strainer from going. Remove the nut and push the tailpiece up to disengage the strainer from the sink. Lift the strainer away from above.
Clean the drain hole to eliminate old plumber’s putty, with a putty knife along with a rag. Screw a new tailpiece onto a brand new strainer. Expand plumber’s putty liberally onto the bottom of the strainer. Insert the tailpiece through the sink hole and let the strainer fall right into position.
Screw on the nut to hold the strainer to the sink from under. Tighten it as much as possible by hand, then complete the job with adjustable pliers. Ask an assistant to stand over the sink and maintain the strainer centered while you tighten the nut, if needed. Wipe the excess putty from around the strainer, using a rag.
Hook up the new pop-up stopper by dropping the stopper into the drain. Insert the lever into the hole at the tailpiece and latch it onto the plate which extends downward from the stopper. Screw on the nut which holds the lever to the tailpiece and tighten it, using pliers. Hold the lever down so that the stopper is all the way up and connect it to the lift pole while it is all the way down.
Slide the compression nut from a brand new P-trap onto the tailpiece using the threads facing downward. Fit a compression ring across the end of the tailpiece using its tapered side facing the end of the pipe. Fit the P-trap onto the pipe and hand-tighten the nut to hold it. Attach the opposite end of the trap to the drain stub-out at the exact same manner.
Close the stopper, fill the sink, then open the stopper and let the water drain at the same time you check the trap. Tighten any connections which leak, utilizing adjustable pliers.