While looking for a reclaimed piece of furniture to use, keep in mind that the average bathroom countertop is 34 to 36 inches in height. When selecting a piece, make sure that the top is strong enough to hold the sink you've chosen to drop in. It's best to have your sink template with you, if possible; you'll be able to make measurements and figure out the best place for the faucets to go. Another thing to consider is the style of the front of the vanity. If the piece you have chosen has drawers, you'll need to retrofit the drawers inside in order to have room for all the plumbing underneath. A vanity with doors instead of drawers works best.
Trace a hole for the sink onto the vanity (Image 1). By doing this first, you'll be able plan the best place for the faucet and the handles. Cut the hole for the sink using an orbital saw (Image 2). Once the hole is cut to the proper size, drop the sink into place (Image 3). With the sink in, you'll be able to determine where the faucet and the handles will look best.
Once you have an idea of where you want the faucet and handles, trace the cartridges for accurately sized holes to drill (Image 1). Cut holes, using the appropriate drill bit, for the faucet and handles for hot and cold water supply. We used 1-inch drill bits for our handles (Image 2). Push the cartridges up through the vanity and attach the handles (Image 3).
Before attaching the faucet, create a waterproof seal using putty around the faucet base that rests on the vanity (Images 1 and 2). Press the base tightly to the vanity and drop the faucet in (Image 3).
Make the cutouts in the back for the plumbing from the wall. Move the vanity flush to the wall to get an idea of where the plumbing needs to come through. Make a reasonable-sized hole: enough space to access the plumbing comfortably in the future. On our retrofitted vanity, we had to take out one of the existing shelves inside the cabinet to make room for the plumbing underneath.
Once you've got all the cuts made for all the plumbing, slide the vanity into place. The p-trap is now ready to be installed. Screw the p-trap onto the drain of the sink from underneath. You should be able to screw this on using just your hand, but you may want to use a wrench to make sure there will be no leakage. After the faucet and p-trap are tightly secured, you will need to attach the water supply line that will eventually be connected to the shutoff valve on the main water supply pipes. Use caution while securing the water supply lines: they are usually just brass or plastic and can be easily stripped. To avoid stripping the lines, try tightening the fittings by hand only.