The best drain unblocker depends on what is causing the blockage. For hair in bathroom plugholes, a thick caustic gel or a plastic drain snake works best. For greasy kitchen sinks, a caustic unblocker or soda crystals in hot water break down the fat. Enzyme cleaners are for slow drains and maintenance, not full blockages. Always try a plunger first, and if several drains block at once, the problem is further down the pipe and may be the water company's responsibility.
A blocked drain feels urgent, which is why people grab the strongest bottle in the shop. Matching the product to the blockage is safer, cheaper and usually faster. Drain unblocker is one of the few strong chemicals worth having in a household cleaning kit, as long as it is used correctly.
First, Work Out What Is Blocking It
| Where | Usual cause | Best first fix |
|---|---|---|
| Bathroom basin, bath or shower | Hair bound together with soap scum | Pull out visible hair, use a drain snake, then a gel unblocker |
| Kitchen sink | Fat, oil and grease mixed with food scraps | Plunger, then soda crystals in hot water or a caustic unblocker |
| Toilet | Wet wipes, too much paper, sanitary products | Toilet plunger; only use a chemical labelled for toilets |
| Several drains, or an outside gully | Blockage in the main drain or sewer | Call your water company or a drainage engineer |
Types of Drain Unblocker Compared
| Type | Best for | Watch out for |
|---|---|---|
| Plunger | Sinks and toilets with a fresh blockage | Cover the overflow hole with a damp cloth so the pressure goes down the pipe |
| Drain snake or hair-removal tool | Hair in bathroom plugholes | Cheap and chemical-free; pull slowly so the hair comes out in one clump |
| Caustic gel or liquid (sodium hydroxide) | Hair, soap and grease; gels sink through standing water | Burns skin and eyes; wear gloves and eye protection |
| Caustic granules | Greasy kitchen drains | Get hot as they work; use exactly the dose on the label |
| Sulphuric acid unblockers | Severe blockages, mainly trade use | Extremely corrosive; best left to professionals |
| Enzyme or biological cleaners | Slow drains, odours and regular maintenance | Work over hours or days; will not clear a full blockage |
| Soda crystals and hot water | Monthly maintenance of kitchen drains | Too mild for a complete blockage |
Kitchen sinks block mainly because of grease. Our guide to the best degreaser for a kitchen explains how alkaline cleaners break fat down.
How to Unblock a Drain Step by Step
- Clear what you can see. Remove the plug or grate and pull out any visible hair or food.
- Plunge. Fill the sink with a few centimetres of water, cover the overflow and plunge firmly ten to fifteen times.
- Try a snake. For bathroom drains, feed a drain snake down and pull out the hair.
- Use an unblocker. If it is still slow, apply one chemical unblocker exactly as the label says and leave it for the full time.
- Flush. Run hot tap water for a minute or two. Avoid boiling water on plastic pipes and toilets.
- Know when to stop. If one dose has not worked, call a plumber or drainage engineer rather than adding more chemicals.
Chemical Safety
Never Mix Unblockers or Plunge After Using One
Two different drain products can react violently in the pipe, so never add a second unblocker on top of the first. Do not plunge after pouring in a chemical, because it can splash back onto your skin and face. Open a window, wear gloves and eye protection, keep children and pets away, and always tell a plumber what you have already used.
Is the Blockage Yours or the Water Company's?
In England and Wales, water companies took over shared sewers and lateral drains that were connected to the public sewer before 1 July 2011. You are generally responsible for the drain that serves only your property and sits within your boundary. The government guidance on the private sewers transfer sets out the details. If neighbours are affected, or the blockage is outside your property, contact your water company before paying for a drainage engineer.
How to Stop Drains Blocking
- Use a sink strainer to catch food scraps before they reach the pipe.
- Bin cooking fat. Thames Water warns that fats, oils and grease set hard in cold pipes, and washing-up liquid does not break them down.
- Catch hair with a plughole cover in the shower and bath.
- Only flush toilet paper. Wet wipes, cotton buds and sanitary products belong in the bin.
- Maintain monthly. A soda crystal and hot water flush keeps kitchen drains running freely.
Our Pick for Preventing Blockages
Kitchen Silicone Sink Filter Strainer
The cheapest drain unblocker is the one you never need. A flexible silicone strainer sits in the plughole and catches food scraps before they mix with grease in the pipe.
View ProductQuick Summary
- Always try a plunger or drain snake first.
- Hair in the bathroom: caustic gel. Grease in the kitchen: caustic unblocker or soda crystals.
- Enzyme cleaners are for slow drains and maintenance.
- One product only, never plunge after chemicals, and wear gloves and eye protection.
- Several drains blocked? Contact your water company.
Shop Cleaning Products
Sink strainers, brushes and cleaners to keep drains running freely.
Shop Cleaning ProductsFrequently Asked Questions
What is the strongest drain unblocker in the UK?
Sulphuric acid unblockers are the strongest, but they are extremely corrosive and mainly used by professionals. For home use, a caustic gel or granule unblocker is strong enough for most blockages.
What is the best drain unblocker for hair?
A drain snake removes hair without chemicals. If hair is too deep to reach, a thick caustic gel sinks through standing water and dissolves it.
Can I use drain unblocker in a toilet?
Only if the product is labelled as suitable for toilets. Most toilet blockages clear with a toilet plunger, which should always be tried first.
Do bicarbonate of soda and vinegar unblock drains?
They fizz, but they mostly neutralise each other and are too weak for a real blockage. They can freshen a slow drain, but a plunger or proper unblocker works far better.
Can I pour boiling water down the drain?
Avoid it with plastic pipes and toilets, as very hot water can soften pipe joints and crack porcelain. Hot tap water is safer.
Who do I call for a blocked drain outside my house?
If the drain is shared with neighbours or is outside your boundary, contact your water company first. If it serves only your property, you will usually need a drainage engineer.
Sources: GOV.UK, Private sewers transfer guidance; Thames Water, Fats, oils and grease.