How to Replace a Bathroom Vanity Drain

Bathroom vanity drains fail for the same reason most plumbing does: they sit underwater day after day, collecting hair and soap, eventually corroding or cracking under the weight of use. A slow drain or visible leak underneath the sink tells you it's time. The good news is that replacing one is straightforward work—you're not touching the wall plumbing or the main vent stack, just unscrewing the assembly that sits under your vanity and installing its replacement. Once you understand how the pieces fit together, you'll find this is one of those repairs that looks more complicated than it actually is.

1. Shut Off Water, Release Pressure. Locate the shut-off valves under the sink—there's typically one for hot water and one for cold. Turn both clockwise until they stop. Open the faucet above to release any remaining pressure in the lines. Leave the drain plug open to let any residual water escape into the basin.
2. Unscrew Supply Line Couplings. Place a towel or bucket under the connection points. Use your adjustable wrench to loosen the coupling nut on each supply line where it connects to the faucet tailpiece. Once hand-loose, unscrew by hand. Water will drip—the bucket catches it.
3. Loosen Trap Slip Nut. The drain trap—the curved PVC or metal pipe under the sink—connects to the tailpiece (the pipe coming straight down from the drain hole) with a slip nut. Use your adjustable wrench to loosen this slip nut. Once loose, slide the trap down and out. You may need to loosen the nut that holds the tailpiece to the sink basin as well.
4. Unscrew Old Drain Body. Working from inside the sink, use a drain wrench or a pair of adjustable wrenches locked together to grip the locknut under the basin rim. Hold the nut steady while you unscrew the drain body itself from above with your other wrench. Once the locknut is loose enough, you can unscrew the drain by hand. Lift the old drain out of the sink.
5. Install New Drain Assembly. Use a rag to wipe away old plumber's putty and debris from the drain hole in the sink. Position your new drain assembly into the hole from above. From underneath, hand-thread the locknut back onto the drain body. Use your wrenches to tighten the locknut—snug only, not gorilla-tight. The drain should sit flush with the sink surface.
6. Reattach Trap Assembly. Screw the tailpiece nut back onto the drain body underneath the sink. Slide the trap back into position and hand-tighten the slip nut that connects the trap to the tailpiece. Use your wrench to snug it down—the nut should be tight enough that it doesn't leak, but not so tight you crack the threads.
7. Restore Water and Check Leaks. Hand-thread the hot and cold supply line couplings back onto the faucet tailpieces. Use your wrench to snug each one down. Turn the shut-off valves counterclockwise to restore water pressure. Turn on the hot and cold faucets and let them run for 10 seconds. Check underneath for any leaks at the supply lines, the tailpiece, and the trap.
8. Verify Drainage Performance. Plug the sink and fill it halfway with water. Unplug and watch the water drain. It should drain smoothly without backing up or gurgling abnormally. Listen for any drips underneath while the water is draining. If everything looks and sounds dry, you're done.