How to Unblock a Drain: 5 Proven Methods for London Homes (2026)
Blocked drain in your London home? Try these five DIY methods before calling a plumber — from boiling water to P-trap removal. With a comparison table, London hard water advice, and when to call a professional.
For a kitchen sink blocked with grease: pour boiling water in three stages, then try baking soda and vinegar. For bathroom or shower drains blocked with hair: use a zip-it tool (£3–£8) to pull hair from the trap. If multiple drains are slow simultaneously, it's a main sewer blockage — call a professional drain engineer.
A blocked drain is one of the most common household plumbing problems in London — and in the majority of cases, you can clear it yourself without calling a plumber. Whether it's a kitchen sink clogged with cooking grease, a bathroom basin blocked with soap scum and hair, or a bath that empties at a trickle, this guide covers every effective method from simplest to most involved.
In 14 years plumbing across London, we've found that the vast majority of domestic drain blockages fall into two categories: grease/food debris in kitchen drains, and compacted hair with soap scum in bathroom drains. The methods below target both, starting with zero cost and working up to tools you'll need to buy or hire.
⚠️ Chemical safety: Never mix drain-clearing chemicals. Combining bleach with caustic soda or other drain cleaners produces toxic chlorine gas. Always read product instructions fully and ventilate the room thoroughly before and during use.
How to Tell If Your Drain Is Blocked
Identifying whether you have a partial or complete blockage — and whether it's localised or affecting your main drain — determines which method to use first.
- Water draining slowly: Earliest sign of a partial blockage building up
- Gurgling sounds: Air being displaced by water around a partial blockage
- Bad smell: Organic matter decomposing in the blockage
- Water pooling: Around the drain in shower or at the basin
- Water backing up into one drain when you use another: This indicates a main line blockage — requires a professional
- Multiple drains slow at once: Also indicates a main sewer issue, not an individual drain problem
💡 London-specific tip: If you live in a terraced house and your neighbour has mentioned drain problems, you may share a common drain run. A blockage affecting shared drainage is the responsibility of Thames Water (if in the public sewer) or both properties (if in a shared private drain). Call Thames Water on 0800 316 9800 for sewer problems outside the property boundary.
Method Comparison: Which to Try First
| Method | Best For | Cost | Time | Effectiveness |
|---|---|---|---|---|
| Boiling water | Kitchen grease blockages | Free | 5 min | High for grease, low for hair |
| Baking soda + vinegar | Soap scum, light organic blockages | £1–£2 | 35 min | Medium — works on partial blockages |
| Cup plunger | Sink and bath blockages | £5–£12 | 10 min | High for solid/compact blockages |
| Zip-it / drain snake | Hair in bathroom drains | £3–£30 | 5–15 min | Very high for hair in trap |
| P-trap removal | Kitchen sink, stubborn blockages | Free (tools needed) | 15 min | Very high — direct access |
| Professional jetting | Main line, deep blockages, limescale | £80–£200 | 30–60 min | Complete — clears any blockage |
Method 1: Boiling Water (Best for Kitchen Grease Blockages)
The simplest first method — and surprisingly effective for kitchen sinks blocked by cooking fat and grease. Boiling water melts and loosens fatty deposits that have cooled and solidified in the pipe. Completely free, zero risk to your pipes (with one exception below), and takes under 5 minutes.
Boil a full kettle
A standard kettle holds 1.5–1.7 litres — the right amount for one treatment. Let it reach a full rolling boil.
Pour in three stages
Pour roughly a third of the kettle directly into the drain. Wait 30 seconds for the heat to work on the blockage, then repeat twice. The pauses allow the heat to penetrate the blockage rather than just flow past it.
Flush with hot tap water
Run the hot tap for 60 seconds at full flow to flush loosened debris through the pipe.
Repeat if needed
If drainage improves but is still slow, a second kettle 10 minutes later is worthwhile. If no improvement after two attempts, move to Method 2.
💡 PVC pipe warning: Do not use boiling water on plastic (PVC) waste pipes — use very hot tap water instead. Boiling water can soften PVC joints over time. If you're unsure what your pipes are made of (very common in London's mix of old and new plumbing), use water from the hot tap at maximum temperature.
Method 2: Baking Soda & White Vinegar (Natural, Safe for All Pipes)
This combination creates a fizzing chemical reaction that breaks up organic matter — effective for bathroom basins and shower drains where soap scum and hair are the main culprits. Non-toxic, inexpensive, and safe for all pipe materials including the old lead pipes still present in some London Victorian properties.
Remove standing water
Scoop out any standing water with a cup. The baking soda needs to reach the drain directly, not dissolve in standing water first.
Pour in baking soda
Pour 125ml (half a cup) of bicarbonate of soda directly down the drain.
Add white vinegar
Follow immediately with 125ml of white vinegar. Cover the drain with a cloth or rubber plug — this forces the fizzing reaction downward into the blockage rather than upward into the room.
Wait 30 minutes
Leave it to work. The fizzing is normal and indicates the acid-base reaction is happening.
Flush with hot water
Run the hot tap at full flow for 60 seconds to flush everything through.
Method 3: Plunger (Kitchen & Bathroom Sinks, Baths)
A cup plunger (flat-bottomed style, not the flanged toilet plunger) creates pressure to dislodge solid blockages. It works best when there is still some water in the basin — the water transmits the plunging pressure directly to the blockage rather than just compressing air.
- Block the overflow opening with a damp cloth to create a proper seal
- Apply petroleum jelly around the plunger rim to improve the seal
- Place the cup plunger over the drain — ensure it forms a complete seal
- Push down and pull up firmly 10–15 times in quick succession
- On the final pull, lift the plunger completely away — the blockage should release
- Run water to test. Repeat 2–3 times if needed
✅ Tip: Applying petroleum jelly around the plunger rim improves the seal significantly, making plunging considerably more effective — this small step is worth the 30 seconds it takes.
Method 4: Drain Snake or Zip-It Tool (Best for Hair Blockages)
For bathroom basins and shower drains — where the blockage is almost always compacted hair and soap scum just below the drain cover — a flexible drain snake or cheap plastic zip-it tool is typically the most effective solution, often clearing the blockage in under 5 minutes.
A zip-it tool (available from Screwfix, B&Q, or Amazon for £3–£8) is a thin plastic wand with backward-facing barbs that snag hair as you pull it back. Keep one under every bathroom sink — at that price, it's one of the best plumbing investments you can make.
Remove the drain cover
Most shower and basin drain covers unscrew or lift directly. Set aside.
Insert the snake or zip-it
Feed it gently down the drain, twisting as you go. Most hair blockages are within 15–30cm of the drain opening — in the trap immediately below the cover.
Hook and pull
Once you feel resistance, twist the snake to catch hair around it, then pull back slowly. The barbs on a zip-it tool grab and bring hair with them. Wear gloves — the material you pull out is not pleasant.
Flush and test
Remove the hair, flush with hot water, and repeat if drainage is still slow. Most bathroom drain blockages come out completely in 1–2 passes.
Method 5: Remove and Clean the P-Trap
For persistent kitchen sink blockages that the above methods haven't fully shifted, the U-shaped pipe under the sink (the P-trap) often contains compacted grease and food debris. Removing and cleaning it takes about 15 minutes and requires no special tools — and you get direct visual access to the pipe beyond.
Place a bucket under the P-trap
The U-shaped pipe will contain water — have an old towel ready as well.
Unscrew the slip nuts
Plastic slip nuts at each end of the curved pipe usually unscrew by hand (anti-clockwise). If tight, use water pump pliers wrapped in cloth to avoid scratching.
Remove and clean
Tip out the contents into the bucket — you may find significant grease buildup. Clean inside with a bottle brush and hot soapy water. Check that the rubber washers are intact before refitting.
Check the pipe beyond
While the P-trap is off, shine a torch up into the waste pipe in the wall. If you can see a blockage, a drain snake inserted at this point will reach it directly.
Refit and test
Reattach the P-trap, tightening slip nuts by hand. Run water at full flow and check all joints for drips before closing the cabinet.
London Hard Water and Your Drains
London water is measured at approximately 300mg/L on the Clarke hardness scale — classified as "very hard" by Thames Water. This is among the highest in England and significantly above the UK average of around 150mg/L. The practical consequences for your drains are real.
Calcium and magnesium dissolved in London water precipitate as limescale inside pipes when water sits still or flows slowly. Over years, this limescale narrows the internal bore and creates a rough surface where grease and debris accumulate far more readily than in smooth new pipes. In a Victorian London home with original lead or cast iron supply pipes, the narrowing effect of decades of limescale can be severe.
Signs of limescale-related drain problems: consistently sluggish drainage across multiple outlets, scale deposits around taps and shower heads, frequent partial blockages that clear temporarily but return quickly. Long-term solutions include fitting a whole-house water softener (£500–£1,200 installed) or periodic descaling with citric acid. Our blocked drains London team can also high-pressure jet limescale from drain pipes, which typically keeps them clear for 1–2 years.
When to Call a Professional Drain Engineer
DIY methods resolve the majority of household blockages. Call a professional when:
- Multiple drains are blocked simultaneously — likely a main sewer line issue
- Water backs up from one drain when you use another (e.g., water appears in the bath when you flush the toilet)
- You can smell sewage inside the property
- Two DIY attempts have not resolved the blockage
- Water is coming up through a ground-floor drain or outside gully
- You live in a flat and suspect the blockage is in shared drainage
Main sewer blockages require professional high-pressure water jetting and sometimes a CCTV survey to locate and resolve the fault completely. See our blocked drains London service for same-day drain clearing across all 32 London boroughs.
Blockage You Can't Shift Yourself?
Our London drain engineers use professional high-pressure jetting and CCTV drain cameras to clear any blockage — same day, all London boroughs. No call-out fee with your booking.
Call 07456 975436Frequently Asked Questions
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Can I use bleach to unblock a drain?
When should I call a plumber for a blocked drain?
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Is baking soda and vinegar actually effective for unblocking drains?
Key Takeaways
- Boiling water in three stages is the fastest first method for kitchen grease blockages — free and takes under 5 minutes
- A zip-it tool (£3–£8) resolves 80% of bathroom and shower drain blockages by physically removing compacted hair
- Never mix drain chemicals — combining bleach with caustic soda produces toxic chlorine gas
- London's hard water (Clarke scale 300mg/L) causes limescale buildup inside pipes, narrowing the bore and accelerating blockages
- Multiple drains slow simultaneously = main sewer line issue — professional jetting required, not DIY
- Thames Water is responsible for sewer line faults from the boundary into the public sewer — call 0800 316 9800 for shared sewer issues
