Quick answer: Start with boiling water, then try a plunger, then a mix of bicarbonate of soda and vinegar left for thirty minutes. If the sink is still blocked, clean the P-trap under the sink or use a drain snake. Avoid harsh chemical drain cleaners where possible, since they can damage older pipework.
A blocked sink is one of the most common household plumbing problems, and thankfully one of the easiest to fix yourself. This guide covers kitchen and bathroom sinks separately, since the usual causes are quite different, then walks through the fixes in order from simplest to most hands-on.
What Causes a Blocked Sink?
Knowing the likely cause helps you pick the right fix straight away.
Kitchen Sinks
Kitchen blockages are usually caused by fats, oils, and grease, often shortened to FOG. These cool and solidify inside the pipe, trapping food scraps as they pass. Over time this builds into a sticky plug that slows or stops the water draining.
Bathroom Sinks
Bathroom sinks are more often blocked by a mat of hair, soap scum, and toothpaste residue that gradually narrows the pipe. Hard water areas can make this worse, since mineral buildup adds to the clog.
Step 1: Try Boiling Water
This is the simplest first step and often clears minor grease-based blockages on its own.
- Boil a full kettle of water.
- Pour it down the drain slowly, in two or three stages, giving it time to work between pours.
Avoid this method if you have plastic (PVC) waste pipes, since very hot water can loosen the pipe joints over time.
Step 2: Use a Plunger
A plunger creates suction that can dislodge blockages further down the pipe than boiling water can reach.
- Clear the sink of dishes or debris.
- Block the overflow hole with a cloth, so the plunger builds proper suction.
- Partially fill the sink with water so the plunger head is covered.
- Place the plunger over the plughole and push down firmly, then pull up, repeating several times with a steady rhythm.
- Check whether the water drains. If not, repeat the process a few more times before moving on.
Step 3: Bicarbonate of Soda and Vinegar
This household mix creates a fizzing reaction that helps break down grease, soap scum, and food residue, without the harsh chemicals found in shop-bought drain cleaners.
- Pour a good amount of bicarbonate of soda down the drain first.
- Follow with an equal amount of white vinegar.
- Cover the plughole with a cloth immediately to keep the fizzing reaction working inside the pipe rather than escaping upwards.
- Leave it for around thirty minutes.
- Flush with hot water from the tap or a kettle.
This combination clears a large share of everyday kitchen sink clogs and is worth trying before reaching for anything stronger.
Step 4: Clean the P-Trap
If the sink is still blocked, the clog may be sitting in the P-trap, the U-shaped pipe under the sink that holds a small amount of water to stop odours coming back up.
- Place a bucket underneath the P-trap to catch any water and debris.
- Loosen the slip nuts at either end of the trap by hand or with pliers.
- Remove the trap and empty it into the bucket, checking for hair, food scraps, or built-up grease.
- Rinse the trap thoroughly, then reattach it, making sure the nuts are hand-tight and not overtightened.
- Run the tap to check for leaks and confirm the water drains freely.
Step 5: Use a Drain Snake or Auger
For a blockage further down the pipe than the P-trap, a drain snake, also called a drain auger, can reach and break up the clog.
- Feed the end of the snake into the drain until you feel resistance.
- Turn the handle to help the tip catch or break through the blockage.
- Slowly withdraw the snake, which should bring some of the debris with it.
- Flush the drain with hot water to clear any remaining residue.
Should You Use Chemical Drain Cleaners?
Shop-bought chemical drain cleaners can work, but they come with real risks. They can damage older metal or plastic pipework with repeated use, and mixing different chemical products, or mixing them with other household cleaners, can produce dangerous fumes. There has been at least one documented UK case where mixing chemical cleaners while trying to unclog a toilet released chlorine gas, requiring evacuation and fire brigade attendance. If you do use a chemical cleaner, stick to one product, follow the instructions exactly, and ventilate the room well.
Preventing Future Blockages
A few simple habits make blockages far less likely to come back.
- Scrape plates and pans into the bin before rinsing, rather than washing fat and food scraps straight down the sink.
- Fit a sink strainer to catch food particles and hair before they reach the pipe.
- Never pour cooking fats, oils, or grease down the drain, even when hot and liquid.
- Pour a kettle of boiling water down the kitchen sink once a week as routine maintenance.
- If you have a waste disposal unit, use it only for the food types it is designed for, not as a general bin.
When to Call a Plumber
Most sink blockages are a straightforward DIY job, but call a professional if the blockage keeps returning within days of clearing it, if multiple drains in the house are blocked at once, which can point to a problem further down the main drain, or if you notice sewage smells or gurgling from other fixtures, since this can indicate a blockage beyond what home methods can reach.
Related Guides
Frequently Asked Questions
How do you unblock a sink without a plunger?
Boiling water followed by a bicarbonate of soda and vinegar mix clears many blockages without any tools. For a deeper clog, cleaning the P-trap by hand is the next step.
Why does my sink keep blocking?
Recurring blockages usually mean fat, hair, or soap scum is building up gradually rather than being fully cleared. Fitting a sink strainer and avoiding pouring fat down the drain will reduce how often it happens.
Can chemical drain cleaners damage my pipes?
Yes, especially with repeated use on older metal or certain plastic pipes. They can also be dangerous if mixed with other cleaning products, so it is best to treat them as a last resort rather than a routine fix.
How do I clean a P-trap safely?
Place a bucket underneath first, then loosen the slip nuts by hand or with pliers, remove the trap, empty and rinse it, and reattach it hand-tight before running the tap to check for leaks.
Is it normal for a bathroom sink to smell after unblocking?
A faint smell for a short time afterwards is common, especially if the P-trap was dry or freshly cleaned. Running the tap for a minute or two usually clears it. A persistent bad smell can mean the trap needs reseating or there is a blockage further along the pipe.
Final Thoughts
Most sink blockages respond well to a straightforward sequence of boiling water, plunging, and a bicarbonate of soda and vinegar soak. Keep chemical cleaners as a backup rather than a first resort, and a sink strainer plus a bit of care about what goes down the drain will keep blockages from becoming a regular problem.