There’s nothing quite as frustrating as standing at your kitchen sink watching water pool around the dirty dishes instead of draining away. Or brushing your teeth while murky water slowly rises in the bathroom basin. A blocked sink is one of those household problems that always seems to happen at the worst possible time.
The good news is that most sink blockages are straightforward to fix yourself without calling a plumber. You don’t need expensive equipment or specialist knowledge. In many cases, you can clear a blocked sink in under half an hour using things you already have in your kitchen cupboards.
This guide explains how to unblock both kitchen and bathroom sinks using proven DIY methods, when to use each technique, and how to prevent blockages from happening in the first place.
What Causes Sinks to Block?
Before you start trying to fix the problem, it’s worth understanding what’s actually blocking your sink. The cause affects which method will work best.
Kitchen Sink Blockages
Fats, oils, and grease (FOG) are the main culprit in kitchen sinks. When you pour cooking oil, bacon fat, or greasy washing-up water down the drain, it’s liquid at first. But as it cools in your pipes, it solidifies into a sticky coating that traps everything else that goes down.
Over time, this builds into a solid plug of grease mixed with food particles, coffee grounds, and soap residue. UK water companies spend £90 million a year clearing FOG blockages from sewers, and most of these start in domestic kitchen sinks.
Food waste makes it worse. Even small particles of rice, pasta, tea leaves, and vegetable peelings get caught in the greasy lining and contribute to the blockage.
Coffee grounds are particularly problematic. They don’t break down in water and clump together to form dense blockages. Never rinse coffee grounds down the sink.
Bathroom Sink Blockages
Hair is the number one cause of bathroom sink blockages. It doesn’t take much. A few strands per day build up over weeks until you have a tangled mat of hair in the U-bend under your sink.
Soap scum binds everything together. Traditional bar soap contains fats that combine with minerals in hard water (particularly in London) to create a hard residue that coats the inside of pipes.
Toothpaste, face wash, and shaving foam add to the problem by sticking to the hair and soap buildup.
Small objects occasionally cause sudden blockages. Toothpaste caps, earring backs, cotton buds, and dental floss can all get lodged in the trap.
Quick Checks Before You Start
Before you try any unblocking methods, do these quick checks:
Is it just one sink or multiple drains? If all your sinks, toilets, and showers are draining slowly, you’ve got a main drain blockage rather than a sink problem. Call a plumber.
Check the water level. If the sink is completely full of standing water, you’ll need to remove most of it before trying certain methods. Use a cup or jug to bail it out into a bucket.
Remove the plug. Lift out or unscrew the sink plug and clean it thoroughly. Sometimes the blockage is just a thick layer of gunk on the plug itself. While it’s out, stick your finger into the plughole (wearing gloves) and pull out any visible hair or debris.
Look for visible blockages. Shine a torch down the plughole. If you can see a clump of hair or an object lodged just below the surface, you might be able to pull it out with needle-nose pliers or tweezers.
If these quick checks don’t solve it, move on to the methods below.
Method 1: Boiling Water
Best for: Kitchen sinks blocked by grease and fat buildup. Simple, fast, and often effective if the blockage is fresh.
Don’t use if: You have PVC pipes under the sink (common in older properties). Boiling water can soften or damage PVC joints. Stick to hot tap water instead.
What you need: A full kettle of boiling water.
How to do it:
- Boil a full kettle
- Pour it directly down the plughole in one steady stream (not all at once, but continuously)
- Wait a few minutes
- Run the hot tap to check if water drains normally
- Repeat if the water’s draining slowly but not fully cleared
Why it works: Boiling water melts fat and grease deposits, allowing them to flow through the pipes. This method works best on early-stage blockages before the grease has solidified completely.
Safety note: Be careful not to splash boiling water on yourself. Pour slowly and steadily.
Method 2: Plunger
Best for: All types of blockages in both kitchen and bathroom sinks. One of the most reliable methods.
What you need: A sink plunger (the flat-bottomed kind, not the toilet plunger with the flange).
How to do it:
- Block the overflow. This is crucial. Use a damp cloth or duct tape to seal the overflow hole completely. If you don’t do this, you’ll just be pushing air and water out of the overflow instead of creating pressure in the pipes.
- Add water if needed. You need enough water in the sink to cover the rubber cup of the plunger (about 5-8cm deep).
- Position the plunger. Place it directly over the plughole, ensuring the rubber cup covers it completely. Press down to create a seal.
- Plunge firmly. Push down hard and pull up sharply. Don’t lift the plunger off the drain. Keep the seal and use vigorous up-and-down motions.
- Do this 15-20 times without stopping.
- Check the results. You should hear a gurgling sound as the blockage clears and feel the pressure change. Run the tap to see if water now drains freely.
Why it works: The plunger creates alternating pressure and suction that loosens and dislodges trapped debris. The vigorous motion physically breaks up the blockage.
Tips: The better your seal on the overflow and around the plunger, the more effective this method will be. Don’t give up after three or four plunges. It often takes sustained effort to shift a stubborn blockage.
Method 3: Baking Soda and Vinegar
Best for: Moderate blockages in both kitchen and bathroom sinks. Natural, non-toxic, and safe for all pipe types. Good for ongoing maintenance too.
What you need:
- 1 cup (250ml) baking soda
- 1 cup (250ml) white vinegar
- A kettle of hot water
How to do it:
- Remove standing water. The sink should be as empty as possible.
- Pour the baking soda down the drain. Get as much as you can directly into the plughole.
- Follow immediately with the vinegar. You’ll see and hear fizzing as the two react. This is normal.
- Cover the drain. Put the plug in or cover with a damp cloth. This keeps the reaction contained in the pipes where you want it.
- Wait 30-60 minutes. The longer you leave it, the better. Some people leave it overnight for stubborn blockages.
- Flush with hot water. Pour a kettle of hot (but not boiling) water down the drain to rinse everything through.
- Repeat if needed. For stubborn blockages, you might need to do this 2-3 times.
Why it works: The chemical reaction between baking soda (alkaline) and vinegar (acidic) creates carbon dioxide bubbles that physically agitate and loosen debris. The fizzing action helps break down organic matter, grease, and soap scum.
Variation: For extra cleaning power, mix the baking soda with 1/4 cup of salt before adding the vinegar. Salt acts as a mild abrasive.
Method 4: Drain Snake (Plumber’s Auger)
Best for: Deeper blockages that haven’t responded to plunging or chemical methods. Particularly effective for hair clogs in bathroom sinks.
What you need: A hand-operated drain snake or auger. Available from DIY shops for £10-£25. Alternatively, a straightened wire coat hanger with a small hook bent in the end.
How to do it:
- Remove the pop-up plug if your sink has one. This gives you clear access to the drain.
- Insert the snake. Push the end of the snake into the drain and keep pushing until you feel resistance. This is your blockage.
- Rotate the handle. Turn the handle clockwise while applying gentle pressure. The snake’s end will either break through the blockage or hook onto it.
- Pull back. Slowly withdraw the snake. If you’ve hooked the blockage, it will come out with the snake. Be prepared for this to be disgusting.
- Flush with hot water. Once you’ve removed the blockage, run hot water for several minutes to clear any remaining debris.
Why it works: The snake’s flexible metal coil can navigate the curved pipes under your sink and physically remove or break apart blockages that are too deep for other methods to reach.
Tips: Be gentle. Don’t force the snake if it’s not moving. Too much force can damage pipes. If you meet solid resistance and can’t push through, you might need professional help.
Method 5: Cleaning the U-Bend (P-Trap)
Best for: Stubborn blockages that nothing else has shifted. This is where most blockages actually are.
What you need:
- Bucket or large bowl
- Old towels
- Rubber gloves
- Adjustable wrench or pliers (maybe – some U-bends are hand-tightened)
How to do it:
- Clear the cupboard. Remove everything from under the sink so you have room to work.
- Place the bucket directly under the U-bend to catch water and debris.
- Loosen the slip nuts. The U-bend (that curved pipe section) is held by two large plastic or metal nuts. Turn them anticlockwise. Many are hand-tight and don’t need tools. If they’re stuck, use an adjustable wrench or pliers.
- Remove the U-bend. Once the nuts are loose, carefully pull the U-bend down and away. Water and gunk will pour out into your bucket.
- Clear the blockage. Take the U-bend outside or to another sink and rinse it thoroughly. Use a bottle brush or old washing-up brush to scrub the inside. You’ll likely find a thick layer of grease, hair, and slime.
- Check the pipes. While the U-bend is off, look up into the pipe that goes into the wall. Shine a torch. If you can see a blockage in there, use a straightened coat hanger or your drain snake to pull it out.
- Reassemble. Put the U-bend back in position and hand-tighten the slip nuts. Don’t overtighten or you’ll crack the plastic.
- Test for leaks. Run water and check underneath for drips. If it leaks, tighten the nuts slightly more.
Why it works: This physically removes the blockage rather than trying to push it through. The U-bend is designed to trap debris and is often where blockages accumulate.
Tips: Take a photo before you start so you remember how it goes back together. Have plenty of old towels ready. This job is messy. Check the rubber washers inside the slip nuts when you remove the U-bend. If they’re worn or cracked, replace them (available cheaply from any hardware shop).
Method 6: Wet/Dry Vacuum
Best for: Removing objects lodged in the drain or pulling out stubborn clumps of hair. Works surprisingly well if you have access to this equipment.
What you need: A wet/dry vacuum (also called a shop vac).
How to do it:
- Set the vacuum to wet mode.
- Create a seal. If possible, create a seal around the vacuum hose and the drain opening. You can use an old cloth or rag to pack around the hose.
- Turn on the vacuum at maximum power.
- Let it run for 30-60 seconds. The suction should pull the blockage out into the vacuum canister.
- Check the canister to see what you’ve removed.
- Flush with hot water to clear any remaining debris.
Why it works: A wet/dry vacuum creates powerful suction that can physically pull blockages out of the pipes, particularly effective for hair clogs and objects.
Note: Only use a wet/dry vacuum designed for liquids. A regular household vacuum will be damaged by water.
Method 7: Commercial Drain Unblocker
Best for: When natural methods haven’t worked and you want to try one more thing before calling a plumber.
Be cautious with: Repeated use can damage older pipes. Never mix different chemical products together. Don’t use if you have a septic tank without checking the label.
What you need: A liquid or gel drain unblocker from a supermarket or hardware shop.
How to do it:
- Read the instructions carefully. Different products have different methods and safety requirements.
- Wear gloves and eye protection. These chemicals are caustic.
- Ensure good ventilation. Open windows.
- Pour the product down the drain as directed.
- Wait the specified time. Don’t cut this short. The chemicals need time to work.
- Flush thoroughly with plenty of cold water (check the instructions – some specify cold, others hot).
Why it works: Chemical drain cleaners use strong alkalis or acids to dissolve organic matter like hair, grease, and soap scum.
Important warnings:
- Never use a plunger after adding chemicals. You’ll splash caustic liquid on yourself.
- Never mix different chemical products. This can create toxic fumes or even explosions.
- Don’t use these products regularly. They can corrode metal pipes and damage older plumbing.
- Keep them away from children and pets.
- If you have a septic tank, check the product is safe for septic systems.
Our view: While commercial drain cleaners can work, we’d always recommend trying natural methods first. They’re safer for you and your pipes.
When to Stop and Call a Plumber
Some blockages need professional help. Call a plumber if:
You’ve tried multiple methods and nothing works. If you’ve plunged, snaked, cleaned the U-bend, and the sink still won’t drain, there’s likely a deeper problem in your drainage system.
Multiple drains are blocked. If your sink, toilet, shower, and bath are all draining slowly, you have a main drain blockage. This needs professional equipment to clear.
Water is backing up elsewhere. If flushing the toilet causes water to come up in the sink, or running the sink causes problems in the bath, you have a venting or main drain issue.
You hear gurgling from other drains. Gurgling sounds when water drains indicate a blockage further down the line affecting air flow in your drainage system.
You smell sewage. A sewage smell coming from your sink suggests a problem with your drain vents or a serious blockage.
You’ve removed the U-bend and the blockage is deeper. Once you get into the pipes in the wall, you need professional tools and expertise.
The sink keeps blocking up regularly. If you’re clearing blockages weekly or monthly, there’s an underlying problem. It might be:
- Incorrectly installed pipes with too shallow a gradient
- Tree roots infiltrating your drains
- Broken or collapsed pipes
- A problem with your main sewer connection
Regular repeat blockages need professional diagnosis and repair, not just temporary fixes.
How to Prevent Sink Blockages
Prevention is genuinely better than cure when it comes to blocked sinks. A few simple habits will save you hours of hassle.
Kitchen Sink Prevention
Never pour fats, oils, or grease down the sink. This is the single most important rule. Let cooking oil cool in the pan, then pour it into an old jar or container and throw it in the bin. Wipe greasy pans with kitchen paper before washing them.
Use a sink strainer. A simple mesh or silicone strainer over your plughole costs less than £5 and catches food particles before they enter your pipes. Empty it into the bin after each use.
Scrape plates thoroughly. Don’t rely on the sink to deal with food scraps. Use a plate scraper or knife to remove all food waste into the bin or compost before washing up.
Never put these down the kitchen sink:
- Coffee grounds (put them in compost or bin)
- Pasta and rice (they swell with water and create cement-like blockages)
- Flour and dough
- Eggshells (they don’t break down and create granular blockages)
- Vegetable peelings
- Cooking oil, fat, or grease
Run hot water after each use. After washing up, run the hot tap for 30 seconds to flush through any traces of grease or soap.
Do a weekly flush. Once a week, pour a full kettle of boiling water down the kitchen sink. This melts any grease deposits before they build up.
Monthly maintenance. Once a month, use the baking soda and vinegar method as preventative maintenance. Don’t wait for a blockage.
Bathroom Sink Prevention
Install a drain cover with fine mesh. This catches hair before it goes down the drain. Clean it after each use. You’ll be amazed how much hair you catch.
Remove hair regularly. Once a week, remove the pop-up plug and pull out any hair that’s accumulated around the stopper mechanism. It’s easier to remove a small amount regularly than a massive clump once it’s become a solid mass.
Switch to liquid soap. Liquid hand soap and shower gel create less scum than traditional bar soap. If you prefer bar soap, make sure you’re rinsing the basin thoroughly after each use.
Don’t use the sink as a bin. Keep a small bathroom bin nearby so you’re not tempted to drop cotton buds, dental floss, or tissues down the sink.
Regular hot water flush. Run hot water for 30 seconds after brushing teeth or washing your face.
Monthly baking soda treatment. Use the baking soda and vinegar method monthly to prevent soap scum and toothpaste buildup.
London-Specific Considerations
If you live in London or another hard water area, you’re dealing with extra challenges.
Limescale builds up faster in hard water. This narrows your pipes over time and gives grease and soap more to stick to. Consider installing a water softener, or at least use the baking soda and vinegar method more frequently (every 2-3 weeks).
Period properties often have older, narrower pipes. What might drain fine in a modern home can cause blockages in Victorian plumbing. Be extra careful about what goes down the drain.
Shared drainage in flats and converted properties means a problem in someone else’s property can affect your drains. If your sink keeps blocking and you’re doing everything right, the issue might be elsewhere in the building. Speak to your building management.
Things NOT to Do
Don’t use excessive force with drain snakes. You can punch through old pipes or push the blockage further down, making it worse.
Don’t mix cleaning products. Bleach and other drain cleaners can react dangerously. Never pour one down after another.
Don’t ignore slow draining. A sink that’s draining slowly is telling you there’s a partial blockage building up. Deal with it now while it’s easy, not in six weeks when nothing will drain at all.
Don’t pour bleach down to “disinfect” drains. It doesn’t unblock anything and can damage pipes. Use for actual cleaning only.
Don’t use boiling water on PVC pipes. Check what your pipes are made of first. Many older properties have PVC waste pipes that can be damaged by boiling water.
Don’t forget to block the overflow when plunging. This is the most common mistake. Without blocking the overflow, plunging is almost completely ineffective.
How Aren Heating & Plumbing Can Help
At Aren Heating & Plumbing, we provide drain unblocking services across London for blockages that won’t respond to DIY methods.
Our Drain Services
Book an engineer: If you’ve got a completely blocked sink causing problems, we’ll get someone to you as quickly as we can.
Professional drain clearing: We use professional equipment including drain rods, power augers, and high-pressure water jetting for stubborn blockages.
CCTV drain surveys: For recurring blockages, we can inspect your drains with a camera to identify the underlying problem. Broken pipes, root infiltration, or incorrect installation all show up clearly on camera.
Repairs and replacements: If the problem is damaged or incorrectly installed pipework, we can repair or replace the affected sections.
Preventative maintenance: We can assess your drainage system and advise on preventative measures to stop blockages happening.
All our engineers carry professional drain clearing equipment, so if we’re attending for another job and you mention a slow-draining sink, we can often sort it on the spot.
When to Call Us
You should call a plumber rather than trying DIY methods if:
- You’ve tried the methods in this guide and nothing’s worked
- Multiple drains are affected
- Water is backing up into other fixtures
- You’re dealing with a recurring blockage
- You suspect a broken or damaged pipe
- You’re not comfortable working on your plumbing
We’ll always be honest about whether you need our help or whether you can fix it yourself.
Get in Touch
If you need help with a blocked sink or any other plumbing issue, give us a call on 0203 807 5822 or visit arenheatingplumbing.co.uk.
We’ll talk you through what’s happening, advise whether it’s something you can fix yourself, and arrange a visit if needed. Our engineers cover all areas of London and carry the equipment to clear most blockages on the first visit.
Don’t let a blocked sink ruin your day. Most are quick and easy to fix, and now you know exactly how to tackle them.
