Why is my bathroom sink not draining?

Causes of bathroom sinks not draining

Blocked bathroom sinks are more common than you might think. In fact, 5.3% of all plumbing and drainage claims at HomeServe in 2024 were for blocked sinks, showers, or baths.

The good news? Once you know what’s causing it, it’s easier to fix and even easier to prevent. Some common culprits include:

• Hair: This is easily the most frequent bathroom sink blocker offender— clumping together and trapping other debris.
• Soap scum: Over time soap can leave behind a sticky residue that builds up in pipes, especially when mixing with the minerals in the water.
• Toothpaste: This may seem harmless, but it can often harden and cling to the inside of your drain.
• Skincare and beauty products: Clay masks, oils, and exfoliants can solidify and slow water flow.
• Foreign objects: Dental floss, hair ties, or even jewellery can accidentally end up in the sink and cause blockages.
• P-trap clog: The P-trap often collects gunk and debris that blocks water flow.
• External drain blockage: Sometimes, the problem isn’t in the bathroom at all. A blockage outside your home can also cause problems with your sink.

5 ways to unblock a bathroom sink

There are several quick and easy methods you can try yourself using everyday items from around the house. Here are five effective ways to get things flowing again:

Plunger

Sometimes, using a plunger is the way to go when clearing a pipe blockage in your sink. Make sure you use a flat-bottomed plunger so you can get a really good seal on your plughole.

1. Seal off the overflow: Use a wet cloth to block the overflow hole. This helps create the suction you need for plunging to work effectively.
2. Fill your sink with hot water: Go up to about halfway to help it form a seal around the plughole.
3. Position the plunger over the plughole: Place the plunger directly over the plughole, ensuring the cup is fully covering it. Remember, a tight seal is key for generating strong suction.
4. Pump the plunger up and down quickly: With both hands, push and pull the plunger rapidly for around 20–30 seconds. Do this vigorously, several times.
5. Remove the plunger and wait: Lift the plunger and see if the water starts to drain. If some or all of the water drains, that’s a good sign that the clog is breaking up.
6. Flush with hot water: If the sink is draining, run hot water for 30 seconds to help clear away any remaining debris. This will also test if the blockage is fully gone.
7. If your sink still isn’t unblocked: Repeat the plunging process a few more times if it’s needed. If this doesn’t work, it’s time to move onto a different method.

Boiling water

Using boiling water is one of the simplest ways to clear minor blockages caused by soap scum, toothpaste, or grease buildup. Here's how to do it:

1. Boil a full kettle (or large pot) of water.
2. Carefully pour the boiling water directly down the drain in a slow, steady stream.
3. Wait a few minutes to see if the water starts draining more freely.
4. Repeat 2–3 times if needed, allowing the water to work through the buildup.

Tip: This method works best for slow drains, not complete blockages. It’s especially effective when combined with baking soda and vinegar beforehand (check out the next method for how to do this).

Baking soda and vinegar

Cleaning your drains with baking soda and vinegar can help to get rid of product buildup and also keep them smelling fresh. You can do this on its own or after removing hair and soap scum:

1. Pour half a cup of baking soda down the drain, followed by 1 cup of vinegar.
2. Plug the drain with a rag to keep the fizzing reaction contained and ensure that the mixture does its job.
3. Wait 15 minutes.
4. Then flush with hot (or boiling) water to wash away any excess soap scum.

Clean the P-trap

The sink’s P-trap is the curved bit of the drainpipe underneath your sink (sometimes called the U-bend). It’s a common spot for gunk to build up, slowing or blocking drainage. Here’s how to check and clear it:

1. Get prepared: Put on rubber gloves, lay down old towels, and place a bucket or washing-up bowl beneath the pipe to catch water and debris.
2. Unscrew the P-trap connectors: Unscrew the slip nuts at either end of the P-trap that holds it to the drain pipe
3. Remove and clean: Take off the P-trap and clear out any buildup inside. Make sure you’re wearing your rubber gloves and that the old towels and bucket are ready to catch water and debris.
4. Reconnect the P-trap: Reattach the pipes, tightening the connectors by hand. Pro plumber’s tip: Don’t over-tighten as you may cause the connectors to crack.
5. Test and check for leaks: Run hot water to see if the issue’s resolved. If it's draining properly, great! Just check for any leaks and tighten if needed.

If the blockage is still there, it might be something more stubborn. In that case, try our drain snake method below to tackle it head-on.

Drain snake

For horribly stubborn blockages, it’s sometimes necessary to bust out a drain snake (also known as a drain auger). This thin, flexible tool reaches deep into the pipes to dislodge tough blockages. Don’t have one? A straightened wire coat hanger with a small hooked end can do the job just fine.

1. Disassemble the P-trap/U-bend: Unscrew the curved pipe under the bathroom sink from in between your basin and the ‘stub pipe’ or ‘stub out’ that travels behind the cabinet wall. Make sure to have a bucket ready for water or sludge, and clean the P-trap if needed.
2. Insert the snake into the stub pipe: Feed it in gently until you feel resistance. Avoid pushing too hard—you don’t want to shove the clog further down. Once the snake hits an obstruction, you’re in business.
3. Break up or hook the blockage: Rotate the drain snake to dislodge debris, or hook and pull it out if using a coat hanger. Keep pulling stuff out until you feel confident that you’ve unblocked your pipe.
4. Reattach the P-trap: Make sure it’s watertight, but don’t over-tighten it. 
5. Flush with hot water: Run hot water to check if you’ve unblocked your sink.

Avoid using harsh drain-cleaning chemicals for your bathroom sink

We always recommend using natural solutions like baking soda and vinegar to clean your drains over commercial drain cleaners.

Harsh chemical cleaners can be corrosive to older pipes, which can damage your plumbing over time. They’re also harmful to the environment, with residues that can affect wildlife and water quality. Plus, their fumes can linger and potentially irritate your skin or eyes during everyday use.

Natural alternatives are safer, gentler, and just as effective for regular drain maintenance.

How do you fix standing water in a bathroom sink?

Standing water in a bathroom sink is due to a full or partial clog. The best way to combat standing water in a bathroom sink is to remove the clog, either by applying a soda and vinegar solution as we explained above. Alternatively, you can remove the plug and manually extract the hair build-up and scum. Sometimes, a combination of the two methods works best.

How to prevent future blockages in your bathroom sink

1. Know where to dispose of the items your drain doesn't like

One of the easiest ways to prevent bathroom sink blockages is by being mindful of what goes down the drain.

• Hair and soap scum: These are the most common culprits of bathroom sink blockages. Use a drain cover to catch hair and clean it out regularly.
• Toothpaste and shaving cream: When using these items, make sure to use water to fully rinse residues away as over time, they can build up and clog pipes.
• Cotton pads, wipes, or tissues: Never flush or wash them down the sink, these should always be put in the bin.
• Skincare product residue (like clay masks or exfoliants): Wipe off excess with a tissue and throw it away before rinsing your face to avoid gritty buildup.
• Jewellery cleaners or nail polish remover: These chemicals shouldn’t go down the drain. Dispose of them according to label instructions or local hazardous waste guidelines.
• Old cosmetics: You shouldn’t wash expired creams or makeup down your bathroom sink. Put them in the bin or check local recycling schemes for cosmetics packaging.

By knowing where these items belong, you’ll reduce the risk of clogs and help to keep your plumbing in good shape.

2. Run hot water down the drain after each time the bathroom sink is used

Keep your drains fresh and free-flowing with a few simple habits: run hot water after each use, use a drain cover to catch debris and empty it daily, pour any leftover boiled water down the bathroom sink to help kill bacteria, and drop in some baking soda once a week (especially useful before going away).

When to call a plumber for a bathroom sink that isn’t draining

If you’ve tried all the methods above and your sink still isn’t draining, it might be time to call a plumber. Signs you need professional help include:

• Persistent clogs
• If the blockage can’t be fixed with DIY methods
• If you suspect that there’s a deeper plumbing issue

And if you’re not comfortable taking apart pipes yourself, it’s always best to leave it to the experts to avoid further damage.

Plumbing and drainage cover you can count on

We get it. Your home is important to you, and when something goes wrong with your plumbing or drains, you want peace of mind. That’s why we offer Plumbing and Drainage cover, helping to protect you in the event of unexpected plumbing problems.

With expert help just a call away, you can relax knowing that we’ve got it covered.