Make a Cutout in the Vanity
Position the vanity in the desired location to check for fit and placement.
Remove the doors and drawers from the vanity for easier installation.
Measure and mark the back of the vanity cabinet for the location of the sink drain. Cut a hole for the drain with a hole saw; Amy used a 3" hole saw to accommodate the 2-1/2" drain. Start the cutout from the back (outside) of the vanity, then finish the cut from the inside of the vanity. This will help avoid splintering the wood.
Position the vanity so the hole lines up with the sink drain.