How to Convert Single-Sink Plumbing for a Double-Sink

modern double sink in bathroom
What You'll Need
Utility knife
Electric drill
Double-outlet valves
Two shut-off valves with dual outlets
Silicone caulk
Plumber's putty
PVC P-trap kit, including compression fittings
PVC T-connector, including compression fittings
Pipe wrench

Double sinks are great for couples and families who might need to use a sink at the same time. Not only does switching from a single sink to a double sink give couples and families more space to get ready for their day, but also double sinks can add a modern, sophisticated look to your bathroom. After choosing your new sinks and vanities, you can easily tie the two sinks into one main drain with the help of the directions below.

Step 1 – Shut Water Off

Before you begin, you should shut the water off with the shut-off valves under the sink. In addition, locate and shut off all water valves going to the house with the main shut-off valve. This step is important for your safety and for preventing a large mess.

Step 2 – Remove the Existing Vanity

Loosen the caulk between the wall and the vanity with a utility knife. Carefully remove the vanity countertop, so that you don’t damage the wall. Remove the screws or nails that hold the old vanity to the wall, and dispose of the old vanity.

Step 3 – Drain the Water and Install Valves

Find the lowest faucet in the house, and drain the water. Then, remove the old bathroom vanity shut-off valves and dispose of them. Install new double-outlet valves by slotting in the supply pipe to the valve. Make sure you pass the nut and compression washer over the pipe. Tighten the nut with a wrench, and then repeat this process for the hot- and cold-water lines.

Step 4 – Turn the Main Supply On

Turn the main water supply back on to check your plumbing for leaks. If you find any, tighten the compression nut again. Tightening the nut should stop the leak.

Step 5 – Install the Faucet

Before you install the new vanity top, install the faucet and drain assembly. Attach the flexible supply lines by using your wrench to tighten the compression nuts to the threaded posts that are on the faucet. Then, put the faucet through the pre-drilled holes in the vanity top and tighten the nut included to keep it in place.

Step 6 – Install the Drain Assembly

To install the drain assembly, apply plumber’s putty under the rim of the drain trim. Push the assembly down through the top of the drain hole and tighten the nut from underneath the vanity until the putty oozes out on all sides. The oozed putty will ensure your drain is sealed. Scrape off excess putty.

Step 7 – Screw the Tailpiece In

Next, screw in the tailpiece that comes from the drain assembly to the drainpipe, and tighten it. Put in the lift lever and the stopper by lining up the lift lever through the hole in the rear of the tailpiece.

Step 8 – Install the Vanity and Apply Silicone

Now, you can install your new vanity. Secure the vanity to the wall studs. Make sure the top is level, and that all valves are clear of any drawers or other obstacles. Then, apply a bead of silicone along the top of the vanity cabinet and set the sink on top.

Step 9 – Connect the Lines

Connect the supply lines to the hot and cold shut-off valves. Tighten the compression nuts with your wrench.

Step 10 – Connect Drain Assembly

Connect the new drain assembly to the old drainpipe. Use a T-connector and a new P-trap. Tighten them.

Step 11 – Test the New Sinks

Turn the shut-off valves back on, and check for any leaks. Turn on the faucet and observe the drain line. Fill the sink up with water, and let the water drain while you check for leaks under pressure.

Step 12 – Caulk the Sides

Apply caulk to the sides and back of the vanity top to the wall. Let it dry for 24 hours before using the new double-sink.