Why is My Bathroom Sink Drain Leaking? Easy Steps To Fix4 min read

Leaking bathroom sinks can be frustrating, gross, and even dangerous. Although leaks are common, many homeowners aren’t sure of the cause or how to resolve the issue. So, why is your bathroom sink leaking, and what can you do about it?

The most common causes for leaking bathroom sinks are loose and damaged compression nuts, poor pipe installation, and clogged traps. In some cases, you can tighten the compression nuts to fix the issue. Other situations require repairs and special tools like Plumbers Tape or Plumber’s Putty.

Don’t panic if your bathroom sink drain leaks or you notice water pools underneath your sink. These are common issues that are often fairly easy to resolve. Let’s take a closer look at the possible causes behind a bathroom sink leak and how you can address them.

Why is the Drain Pipe Under the Sink Leaking?

Bathroom sink drainage
Typical bathroom sink drainage setup

A leaky drain pipe under the sink is a common issue that’s equally frustrating. The most common causes for leaky drain pipes are loose or damaged decompression nuts. However, faulty pipe installations and clogged sink traps can also cause issues.

Let’s go through each of these causes so that you can determine if it’s the one you’re dealing with.

Loose or Damaged Compression Nuts

Loose, damaged, or faulty compression nuts are common culprits behind drain pipe leaks. Loose compression nuts don’t seal the sink pipes properly, causing water to leak out. The nuts can become cracked and worn out over time, allowing water to slowly seep out.

But as you check these metal or plastic fasteners on your plumbing lines, be careful not to over-tighten them. Over-tightening a loose compression nut can cause it to crack, so be sure that you tighten the component just enough to form a good seal.

Poor Pipe Installation

In some cases, poor or faulty pipe installations can cause drain pipes to leak. Your pipes may be fitted together incorrectly or include a combination of sizes and improper lengths.

In these cases, pressure will build up at the joints and cause leaks. You may need to call a professional plumber to resolve the issue if you don’t have prior experience. This is rarer, but is more likely in older buildings.

Blocked Traps or vents

Clogs and blockages can also cause pressure to build. Excessive stress can cause your pipes to crack or break at the joints, leading to leaks.

In some cases, liquid drain cleaners can further erode damaged faulty joints and damaged pipes. You may need to call a professional plumber to resolve these issues. Though a good first step is to try a drain snake (on Amazon).

If your sink has a vent, or you suspect a vent may be the issue, have a look at our article on sink vents to get up to speed.

Tools That Can Help Stop a Leaking Drain Pipe

If you don’t have the time or resources to call a plumber, you may want to stop a leaky drain pipe on your own. Fortunately, this is a fairly common issue that many homeowners can resolve with a little bit of elbow grease.

You’ll need a few tools before you get started, including the following:

Materials like Plumbers Tape can be helpful, as they work with nearly any fitting and ensure a tight seal. Plumbers Putty, on the other hand, is a stretchable substance that can mold easily around components that need a tight seal.

Other tools like adjustable wrenches and pliers can help you tighten parts. You’ll also want a bucket and a few rags to clean up any excess water. Lastly, you’ll want to purchase any replacement components if necessary.

All of these tools and parts can easily be found at your local hardware store or online for affordable prices.

Fixing The Leak

Once you’ve got the necessary supplies, it’s time to fix your leak. Proceed with the following steps:

1. Tighten the Nut if Needed

In many cases, you can fix a leaky drain pipe by simply tightening the nut. In these situations, you won’t need any replacement components or Plumber’s Putty and tape. Inspect the nut underneath your sink and see if you can tighten it another half-turn or so.

Compression nuts under bathroom sink
Compression nuts under bathroom sink

If you can tighten it, turn on the water and see if there are any leaks. If there are still leaks, you’ll need to move on to the following troubleshooting method below.

2. Assess the Parts for Damage

Still have leaks after tightening the pipe nut? The first step to repairing a leaky pipe underneath your sink is to assess the parts for any cracks, breaks, or damage. For instance, you may have a gasket or rubber seal that’s damaged and causing leaks.

You can take all the components apart, including the drain pipe and drain outlet flange, to inspect them for damage.

3. Replace the Seals Using Plumber’s Tape

If you take everything apart and notice zero signs of cracks or damage, you may not require any replacement parts. Instead, you may need to reinstall your sink using Plumbers Tape or Plumbers Putty to resolve the issue.

Plumbers tape under bathroom sink
Here you can see my plumbers tape is worn and fraying, and is worth replacing

Here are some basic instructions you can follow after taking everything apart, cleaning, and inspecting for damage:

  1. Apply a ½” thick ring of Plumbers Putty to the underside of the top flange of your sink drain.
  2. Next, add Plumbers Tape to the threads of the sink drain.
  3. Apply enough Plumbers Tape to cover the threads near the site where the nut will be tightened.
  4. Take the compression nut and spin it all the way down the threads.
  5. Insert your drain into the sink hole, ensuring it’s centered.
  6. Install the nut and the sealing washer. Tighten the nut and seal the washer.
  7. You may notice excess putty oozing out until the nut and washer are fully tightened. Remove any excess putty.
  8. Now, apply Plumbers Tape to any sites of the drain pipe that have threads.
  9. Reinstall your drain pipe. Ensure it’s entirely centered and not too tight.
  10. Turn on the faucet and inspect for any leaks underneath the sink.

Still Leaking? You May Need to Make a Repair

If you tightened the compression nut, took your sink apart, and reinstalled it, and you’re still noticing leaks, you may need to repair a much larger issue. You may have a damaged or cracked pipe that needs to be worked on.

In some cases, it’s better to call a professional plumber for assistance instead of working on the issue yourself.

When to Call An Expert

If you tried all of the troubleshooting methods above and your drains are still leaking, it may be time to call an expert. A leaky drain could be a sign of other significant issues, like a rapid drainage line leak, sewer line leak, damaged pipes, or other problems.

A professional plumber will have the tools and experience to diagnose the issue and act accordingly.

There are some tips you can use when you call an expert to ensure you get the best service for the most affordable rates, including the following:

  • Call multiple plumbers.
  • Request a quote for the service call.
  • Request an estimate of the repair cost.
  • Request to speak to the plumber if possible.

Using some of the tips above can help you find the best rates for your issue. Don’t be afraid to shop around and request estimates before settling on a plumber to hire.

Provide as many details as you can about your problem to ensure you receive the best quote and service available.

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