bathroom sink leaking underneath - woman fixing

4 Ways to Fix a Bathroom Sink Leaking Underneath (Fast & Easy!)

ByDino Pelle

We’ve all experienced a bathroom sink leaking underneath. It’s terribly frustrating. Even worse, it can cause water damage to your floors and subflooring if not dealt with quickly.

So, today, I’m going to show you how to fix 4 problems that cause leaks under a bathroom sink.

How to Fix a Bathroom Sink Leaking Underneath

This instruction won’t cover every type of leak you’ll find under your sink. But it will cover four of the most common problems we come across as emergency plumbers. To be prepared to tackle any of them, you’ll want to make sure you have access to:

parts diagram of bathroom sink leaking underneath
This diagram points out all the major parts of a bathroom sink so you can identify how to fix the leak underneath.

1. Bathroom Sink Leaking Underneath at the Drain Body

If water is leaking from the point where the pivot rod enters the drain body, here’s what to do:

  • Tighten the retaining nut with an adjustable wrench or slip-joint pliers.
  • If it still leaks, unscrew the retaining nut, slide the pivot rod out of the drain body, and replace the washer or gasket under the retaining nut.
  • If leaks continue to persist and the lift mechanism is badly worn, replace its parts or the drain body and pop-up assembly.

2. Bathroom Sink Leaking Underneath at the Trap

  • Tighten all slip nuts and locknuts a quarter-turn. Be firm but not aggressive.
  • Wipe the entire trap assembly with a dry rag, then run the basin full of water through the drain to test it.
  • If leaks appear around the slip nuts, remove the trap bend, then the trap arm, and replace the washers.
  • Replace the bend or arm if it is damaged or corroded.
  • If the tailpiece or sink flange also leaks, go to step 3 below before installing the trap.
  • If a new trap arm is too long to fit into the drainpipe, trim off the excess length with a hacksaw to fit. The trap arm should extend about 1.5 inches into the adapter or stub-out.

3. Bathroom Sink Leaking Underneath at the Tailpiece

  • Unscrew the tailpiece with a wrench. If it’s made of brass, it can be easily crushed so try to unscrew those by hand.
  • For a better grip, here’s a pro tip: slip a wide rubber band onto the tailpiece. This will keep your hand from slipping while trying to loosen the tailpiece.
  • If the tailpiece is stubborn, remove it with a pipe wrench and buy a replacement of the same length.
  • An old tailpiece might crumble; use the long-nose pliers to twist out any remaining pieces from the threads of the drain body.
  • Before installing a new tailpiece, wrap Teflon tape (also called thread seal tape or plumber’s tape) around the threads and replace the trap’s slip nut and washer.

4. Bathroom Sink Leaking Underneath at the Sink Flange

A worn washer or cracked putty under the sink flange might allow water to seep below the sink. Here’s what to do to prevent this kind of leak.

  • Remove the trap bend, if you haven’t already done so.
  • Then remove the drain body and free the flange from the sink.
  • Apply a thin strip of plumber’s putty under the lip of the flange. See related resources below.
  • Reinstall the drain body and pop-up assembly.
  • Wipe away any excess putty around the flange.
  • If leaks persist, tighten all connections one-quarter-turn at a time.

Final Thoughts

Leaks underneath a bathroom sink are quite common. We get calls every day to fix them. Although you need to attend to them quickly, you can handle many of these yourself with just a little knowledge and plumbing experience.

Along with the resources below, this video will show you how to properly use plumber’s putty.

Call 1-Tom-Plumber

Don’t hesitate to contact us here or call us at 1-Tom-Plumber (1-866-758-6237) if you have water leaking underneath your bathroom sink (or anywhere else). 

1-Tom-Plumber’s certified team of plumbers and drain technicians respond immediately to any emergency plumbing, drain cleaning, or water damage problem. We also handle the excavation of underground water lines and sewer main lines. Our immediate-response team is available every day and night of the year, even on holidays.

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