Begin by clearing everything out from under the sink cabinet to give yourself ample working space. Place a bucket and some old rags or towels under the P-trap and water supply lines to catch any residual water that will spill during disconnection. Turn off the hot and cold water supply by turning the handles on the shutoff valves clockwise until they are fully closed. Once the valves are closed, turn on the old faucet to relieve any pressure in the lines and confirm that the water is completely off.

Using an adjustable wrench or basin wrench, carefully loosen the coupling nuts that connect the hot and cold water supply lines to the threaded tailpieces on the bottom of the old faucet. Turn the nuts counter-clockwise. Be prepared for a small amount of water to drip out into the bucket. Once the nuts are loose, you can usually unscrew them the rest of the way by hand.

Locate the pop-up drain's lift rod mechanism. You will see a horizontal pivot rod connected to the drain pipe with a clip. Squeeze the spring clip to release the horizontal rod from the lift rod strap. Then, using channel-lock pliers, unscrew the retaining nut that holds the pivot rod in the drainpipe and pull the rod out. The pop-up stopper can now be lifted out from the top of the sink.

This is often the most challenging step. From underneath the sink, use a basin wrench to loosen and remove the mounting nuts that secure the old faucet to the sink deck. These nuts can be plastic or metal and are often corroded and difficult to access. Turn them counter-clockwise to loosen. Once the nuts are removed, you can lift the old faucet assembly straight up and out of the sink from above.

With the faucet removed, focus on the old drain. From underneath the sink, use channel-lock pliers to unscrew the large slip nut connecting the drain tailpiece to the P-trap. Then, unscrew the large mounting nut that holds the drain flange against the sink. Once this nut is removed, push up on the drain assembly from below and pull the old drain flange out from the top of the sink basin.

With all old hardware removed, thoroughly clean the top surface of the sink where the faucet base and drain flange were located. Use a plastic putty knife to gently scrape away any old, hardened plumber's putty or sealant residue. Avoid using metal scrapers that could scratch the sink's finish. Follow up with a non-abrasive cleaner and a rag to ensure the surface is perfectly clean and dry for a good seal with the new components.

First, place the gasket or base plate (included with the new faucet) onto the sink. Carefully feed the new faucet's tailpieces and mounting studs down through the holes in the sink deck. From underneath, slide on any supplied washers and thread the mounting nuts onto the studs. Hand-tighten the nuts first to position the faucet correctly from above, then use the basin wrench or supplied tool to snug them down securely. Do not overtighten.

Check your faucet instructions: some modern drains use a rubber gasket instead of putty. If putty is required, roll a rope of plumber's putty about 1/4-inch thick and place it under the lip of the new drain flange. Insert the flange into the sink drain hole from above. From below, slide the rubber gasket and mounting nut onto the drain body and tighten it firmly by hand, then give it a final quarter-turn with channel-lock pliers. Clean any excess putty that squeezes out. Insert the pivot rod through the hole in the drain, making sure it passes through the hole in the stopper. Attach the lift rod and strap, and test the pop-up mechanism.

Connect your new (or existing) flexible supply lines to the hot and cold faucet tailpieces. The connections are typically hand-tightened, then given a final quarter-turn with an adjustable wrench. Do not overtighten. Connect the other end of the supply lines to the corresponding hot and cold shutoff valves in the same manner. Ensure the hot line connects to the left side of the faucet and the cold to the right.

Before turning the water on, double-check that all connections are snug. Unscrew the aerator from the tip of the new faucet spout to prevent any debris from clogging it. Place a rag over the spout opening. Slowly turn the water back on at the shutoff valves. Let the water run for a minute to flush any sediment out of the lines. While the water is running, use a flashlight to meticulously inspect every connection point for leaks: at the shutoff valves, at the faucet tailpieces, and around the drain assembly. If you find a leak, turn the water off and gently tighten the connection another 1/8 to 1/4 turn. Once you are certain there are no leaks, turn the water off, screw the aerator back on, and your project is complete.