How to Install Bathroom Vanity with Sink? | Step-By-Step Swap

Installing a bathroom vanity with sink takes a weekend and basic tools—shut off the water, pull the old unit, set the new one level and anchored, then reconnect and test.

For the full breakdown, see our best 42 Inch Vanity With Sink guide.

Swapping a tired bathroom vanity ranks among the most satisfying DIY upgrades, and the process is forgiving enough for a careful beginner. The whole job boils down to three phases: disconnecting the old vanity, setting and securing the new one, and reconnecting the plumbing without leaks. Whether you’re replacing a battered cabinet or upgrading to a double sink, the sequence below walks through each step in the order it needs to happen. If you’re still shopping for the centerpiece, a roundup of the best 42 inch vanity with sink can narrow down the options before you start measuring.

Preparing the Space and Shutting Off Water

Turn off the water supply before touching anything. Find the shutoff valves under the sink—usually two small valves on the wall—and close them. If there are none, shut off the main water valve for the house. Open the faucet afterward to relieve pressure and drain the lines. Put a bucket under the P-trap, the curved pipe below the sink, then loosen and remove it. Follow by disconnecting the hot and cold supply lines from the shutoff valves with an adjustable wrench.

Clear everything under the vanity and protect the floor with a drop cloth. Cut through the caulk where the backsplash meets the wall using a utility knife, then look inside the cabinet for screws holding it to the wall studs. Remove those screws and gently pull the old vanity away from the wall, taking care not to damage the supply lines or drain pipe behind it.

Before buying a replacement, confirm the rough-in height and location. The new unit needs to sit where the existing water supply and drain line reach, so measure the distance from the wall and floor to those connections. Choosing a different vanity footprint might mean moving the plumbing, which turns a DIY swap into a plumber’s job.

Setting and Securing the New Vanity

Position the new vanity against the wall and check it with a level. Bathroom floors are rarely perfectly flat, so slide shims under the cabinet until it sits level both side-to-side and front-to-back. Then locate the wall studs with a stud finder and mark their positions inside the cabinet. Drive screws through the back rail of the vanity into each stud. If a stud doesn’t line up correctly, use wall anchors rated for the weight instead.

Leave the shims in place and trim the excess flush with the cabinet base using a utility knife. At this stage, verify the location still lines up with the water supply and drain. Hiding a mismatch behind a finished cabinet is one of the most common and costly mistakes in this project.

Installing the Faucet, Drain, and Sink Top

Manufacturers typically want the faucet and drain installed before the sink top is set into place. Lay the top upside down on a padded surface, fit the faucet through its mounting holes, and tighten the nuts underneath. Attach the drain assembly to the sink basin, keeping the overflow hole facing forward. Apply a bead of silicone caulk around the cutout edge or the sink’s underside, then lower the top into position. Use the sink clips or brackets if your model includes them; instructions for the specific vanity will identify which sealant type works—silicone caulk, siliconized acrylic caulk, or silicone adhesive.

Once the top is seated, connect the supply lines to the faucet tails, then hook the P-trap back up to the drain stub coming out of the wall. Hand-tighten the nuts first and snug them with a wrench only if needed—forcing them can crack the fittings. Avoid stressing the plumbing into alignment; if the drain height or valve positions don’t match, the rough-in needs adjustment before the final hookup. Hot water sits on the left and cold on the right for standard faucet hookups, so cross-check the lines before tightening.

Testing for Leaks and Final Sealing

Turn the shutoff valves back on slowly and open the faucet, watching every connection for drips—under the sink, at the shutoff valves, the P-trap, and the faucet base. Let the water run for a few minutes, then check again. Tighten any leaking connections gently rather than cranking them, and test once more. Apply a final bead of caulk along the backsplash where the vanity meets the wall, then smooth it with a wet finger or a caulk tool. A correctly anchored, level vanity with sealed seams and dry plumbing is the whole job.

If the current plumbing rough-in and your new vanity simply won’t line up—say the drain sits too low or the supply valves land in the wrong spot—stop and adjust the rough-in before finishing. Patience at this stage saves a wall patch and a repair bill.