Bathroom Sink Drain Pipe Is Leaking – How To Fix – What To Check?

I installed a new bathroom faucet and it came with a new drain pipe and sink drain outlet flange. The faucet works great but the drain pipe is leaking under the sink. It is leaking down into my bathroom cabinet and getting everything wet. The leak is coming from where the plastic nut on the drain pipe meets the bottom of the bathroom sink. I installed the sink drain pipe with the included rubber sealing washer and gasket but without any plumbers tape or plumbers putty. Is that why it is leaking?

Bathroom sink drain leaking at bottomBathroom sink drain leaking at bottom

If the drain pipe under your bathroom sink is leaking, you may need to simply re-tighten the nut. If no Plumbers Putty was used when installing the drain outlet flange in the sink, this is another reason it may be leaking. You may also have the gasket or rubber sealing washer that goes between the nut and the sink overtightened and this is causing the leak. The gasket or rubber sealing washer may not be completely flat and therefore not sealing. Check to see if you are able to tighten the nut with another half turn or so and check for leaks. If no matter how tight the nut is and it still leaks, take everything apart including the drain pipe and the drain outlet flange in the sink.

After taking the bathroom sink drain outlet flange and drain pipe out, inspect all parts to see if it may be cracked or if the plastic or metal threads are stripped. Is the gasket, rubber sealing washer, drain outlet flange, drain pipe, or nut damaged? If the drain pipe and the components are not damaged, you will NOT need any new parts but you will need a few extra items to make sure it does not leak before reinstalling.

2 items that will help stop a leaking sink drain pipe:
Plumbers Tape (Works with any fitting needing a high quality seal – Ensures a secure and tight seal)
Plumbers Putty (Flexible stretchable compound – Molds easily – Will not harden, crumble, crack or shrink)
NOTE: These items are optional but are used in professional plumbing to avoid leaking pipes. Use Plumbers Tape on all threads to create a tight water seal.

Pipe Sealant Tape - Plumbers TapePipe Sealant Tape – Plumbers Tape

Plumbers PuttyPlumbers Putty

What could be the cause of the water leak under the sink?
1 – Water may leak in between the threads on the nut and the drain pipe if no plumbers tape was applied.
2 – The rubber sealing washer or o-ring may be squeezed excessively tight causing leakage.
3 – The nut may not be tight enough and water is simply coming through.
4 – The drain pipe is off center and therefore a tight seal is not possible.
5 – The drain pipe is cracked and water is coming through the crack.
6 – The fitting for the pop-up sink assembly is not tight.
7 – The sink drain may leak if no Plumbers Putty was used.

Bathroom sink drain parts identification 1Bathroom sink drain parts identification 1


Bathroom sink drain parts identification 2Bathroom sink drain parts identification 2


Bathroom sink drain parts identification 3Bathroom sink drain parts identification 3

How to reinstall the sink drain WITHOUT any leaks… (Be sure all parts are removed, clean, and not damaged)
1 – Add a 1/2″ thick ring or rope of Plumbers Putty to the underside of the top flange of the sink drain. (Warm the putty up with your hands first to make it easier to use – Be sure the Plumbers Putty is in a continuous circle)
2 – Apply some Plumbers Tape to the threads of the drain.
3 – Use enough Plumbers tape to cover the threads near the area where the nut will be positioned when fully tightened.
4 – Spin the nut all the way down or off of the threads.
5 – Insert the drain back into the sink hole and be sure it is centered.
6 – Install the nut and the sealing washer and tighten. (The excess putty will ooze out under the top flange until it is fully seated to the sink)
7 – Remove the excess putty from in the sink.
8 – Add Plumbers Tape to any areas of the drain pipe that has threads.
9 – Reinstall the drain pipe making sure it is centered and not overtightened.
10 – Run the bathroom faucet and check for water leaks under the sink.

Have questions on fixing or repairing a leaking sink drain? Leave your question below and we will assist you to stop your drain from leaking.

More "Do It Yourself" Tips, Tricks, Ideas, Repair:

Appliance Replacement Parts Center Online

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