In this video, This Old House plumbing and heating expert Richard Trethewey shows how to install a new sink into an existing vanity.
1. Turn off the water to the vanity. Then, place the new sink upside down on top of the vanity.
2. Measure and mark the final position of the sink onto the vanity top by tracing around the perimeter of the sink.
3. Place the sink's paper template centered on the sink outline.
4. Drill a ⅜-inch-diameter hole through the vanity top; be sure to drill hole inside the template lines.
5. Use a jigsaw to cut the sink hole into the vanity top.
6. Cut into the existing PVC drainpipe using a hacksaw.
7. Wrap Teflon tape around the threads of the drainpipe stub-out that's protruding from the wall.
8. Thread a PVC female adapter onto the stub-out.
9. Cut and dry-fit together all the PVC pipe and fittings needed to complete the drainpipe for both sinks.
10. If necessary, use a drill and hole saw to bore holes through vertical dividers inside the cabinet for running the pipe.
11. Glue together the PVC pipe and fittings using PVC primer and cement.
12. Use a propane torch to remove the existing shut-off valves from under the existing sink.
13. Solder a copper T-fitting onto each water-supply pipe.
14. Complete the water-supply piping, installing a hot- and cold-water shut-off valve under each sink.
15. Attach the drainpipe and faucet to the new lavatory sink. Be sure to seal faucet with plumber's putty.
16. Apply a little pipe-joint sealant to the threaded end of the flexible water-supply line.
17. Connect the water-supply lines to each faucet.
18. Install the pop-up assembly to the sink.
19. Run a continuous bead of silicone sealant around the underside of the flange on the sink.
20. Set the sink down into the hole cut in the vanity top.
21. Wipe away any excess silicone sealant from around the sink. Allow the sealant to cure overnight.
22. Attach the PVC drainpipes to each sink, and then connect the hot- and cold-water supply lines to the shut-off valves.
23. Turn the water back on and test your work.