Turn off the water supply and empty the lines. The shutoff valves are usually located in the cabinet under the sink. Turn both the hot and cold valves clockwise until they resist further turning. Then, turn on the hot and cold faucet taps to empty the faucet lines. If the shutoff valves won’t stop the flow of water completely, you’ll have to replace them. Unless you have some plumbing experience, this may be a job best left to a professional.
Disconnect the P-trap portion of the drain pipe. If the P-trap is made of PVC, loosen the slip nut that connects it to the underside of the sink drain by hand. If the P-trap is made of metal, loosen the connecting nut with channel locks.
You don’t need to remove the P-trap to replace the sink, but you may want to remove it temporarily so you can clear it of debris. To take it out, unscrew the nut (by hand or with channel locks) that connects the bottom of the P-trap to the drain line below. Place a bucket or heavy towel at the bottom of the cabinet to catch any dripping water.
Unfasten the hot and cold water lines with a crescent wrench. These are flexible lines that run from the shutoff valves to the underside of the faucet. Disconnect them right above the shutoff valves. Some types may have nuts you can loosen by hand, but you’ll often have to use a crescent wrench. You can reuse these water lines if you want—just disconnect them from the underside of the sink later, then reattach them during installation. But this is also a good time to replace them.
Measure the dimensions of the old bathroom sink with a measuring tape. If you want to reuse your existing countertop, makes sure you get a new sink that will fit in the same spot as the old one. Write down the length, depth, and width of the sink, as well as the length and width of the countertop. You’ll likely have to replace the countertop as well if you want a new sink that’s a different size.
Buy your new sink at a home improvement store. Bring the measurements of the old sink and countertop with you. This helps to ensure you purchase the correct size before putting in a bathroom sink. Make sure the replacement sink is the same type (top-mount or undermount) as the old one. Ask an employee for assistance if you need help selecting a new sink. Most bathroom sinks are still made of ceramic, but there are other options, and many colors to choose from beyond the traditional white.