Carefully measure the height and width of your new vanity. Determine where you want to position it and mark the edge locations with vertical lines. Now, measure and mark up from the floor in three places the height of your vanity. Use the highest mark and draw a level line through it, joining the two vertical lines. You now have an exact outline for the placement of your vanity.
Carefully measure the locations of the water pipes and drain lines coming out of the wall and transfer those measurements onto the back of your vanity. Use a hole saw (at least 1/2″ larger than the pipes) and drill holes for your water lines. Cut the cutout for the drain with a larger hole saw or a jigsaw.
Verify where at least one stud is in the wall behind your new vanity, measure and mark its location on the vanity nailer, and drill a pilot hole for the 3″ screw that will hold it in place.
Finally, Installing the New Vanity
Minimize the chance for damage (and make the vanity lighter and easier to move) by taking out any drawers and removing the doors.
Protect your floors and move the vanity into position, then slide it into place with the water and drain pipes coming through the holes you cut in the back. Check that the cabinet is level (both side to side and front to back), and use shims to level it if necessary. Once the vanity is level, attach it to the wall using 3″ screws.
If your new vanity has a built in or molded sink, you will need to install the faucet before you put the top in place. Start by putting the faucet through the precut holes and hand tighten them. Now turn the vanity top over and use a wrench to firm them up. Attach flexible water supply lines to the base of the faucet and the tail pipe to the sink drain. Finally spread a bead of silicone caulk all around the edge of the countertop, then turn it over and position it on the vanity with the backsplash tight against the wall.
If you’re putting a separate sink into your new vanity, you will need to install the countertop first, then install the faucets to the sink, and finally put the sink into the countertop.
Attach the flexible feed lines to the water supply valves and connect the sink tailpiece to the trap and drain. Run a small bead of caulk around the base of the faucet and where the vanity top butts against the backsplash, and then install moldings around the base of the vanity. Finally, turn the water back on and check for any leaks.