How to Install a New Bathroom Vanity Sink

Replacing a bathroom vanity sink is one of those projects that looks intimidating until you realize it's mostly about disconnecting old plumbing, sliding out a cabinet, and reconnecting the new one. The actual mechanics are straightforward—water comes in through two lines, waste goes down through one drain. The part that trips people up isn't the plumbing; it's the cabinet removal and making sure everything sits level and tight before you turn the water back on. A new vanity transforms how a bathroom feels and functions. You're not just upgrading the sink; you're getting fresh storage, a cleaner look, and a chance to fix whatever was wrong with the old setup. This guide walks you through the whole thing in order, so nothing gets missed and you don't have to turn the water off twice.

1. Shut Off Water First. Locate the shutoff valves under the sink—one for hot, one for cold. Turn them clockwise until they stop. Open the faucet to release any pressure in the lines. If the valves are stuck or leaking, shut off the main house water supply instead.
2. Free All Water Lines. Place a bucket under the supply lines where they connect to the faucet. Use an adjustable wrench to loosen the compression nuts on both hot and cold lines, then unthread them by hand. Loosen the large nut connecting the P-trap (the curved pipe under the sink) to the drain tailpiece, then slide it out of the wall opening.
3. Extract Old Cabinet. Check underneath the sink and around the top edge for screws or brackets bolting the vanity to the wall or floor. Unscrew everything you find. Gently rock the cabinet side to side to break any caulk seal, then pull it straight out. If it's wedged tight, use a pry bar between the cabinet and wall to ease it out.
4. Level and Bolt Down. Slide the new cabinet into place. Check that it's level front-to-back and side-to-side using a torpedo level on the countertop. Shim underneath with wooden shims until it sits perfectly level. Once level, bolt the cabinet to the wall studs and to the floor through the pre-drilled holes, using lag bolts or screws appropriate to your wall type.
5. Mount Sink and Faucet. If your new vanity came with a pre-drilled countertop, skip this. If not, use the faucet and sink templates to mark holes. Drill the faucet holes and sink opening if needed. Set the faucet into the countertop holes and tighten the mounting nuts underneath. Place the sink into the countertop opening and secure it with the provided clips or adhesive, depending on the model.
6. Reconnect All Lines. Thread the hot and cold supply lines back onto the faucet inlet ports and tighten the compression nuts by hand, then snug them with a wrench—don't over-tighten. Reconnect the P-trap by sliding the nut back onto the drain tailpiece and the wall drain opening, tightening by hand then a half-turn with a wrench. Leave a slight gap; you're not clamping it, just sealing it.
7. Verify Zero Leaks. Turn both shutoff valves counterclockwise to restore water pressure. Let the faucet run for 10 seconds. Watch under the sink for drips at the supply connections, the faucet base, and the P-trap. If you see a drip, tighten that connection one-quarter turn and check again. Run water into the sink and watch it drain.
8. Seal and Cure. Run a bead of silicone caulk around the seam where the countertop meets the wall and where the faucet base meets the countertop. Use a wet finger or caulk tool to smooth it into the gap. Let it cure per the manufacturer's instructions (usually 24 hours) before exposing it to water.