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How-To Guide

How to Unblock a Drain

Most blocked sinks, baths, and toilets can be cleared at home with a plunger, hot water, or a quick clean of the U-bend β€” before you pay anyone. This guide walks through the safe methods in order, shows you the warning signs that mean stop and call a pro, and explains what professional drain unblocking costs.

7 minute read Β· Updated June 2026 Β· UK guidance

Quick answer

To unblock a drain yourself, work from gentlest to strongest: (1) flush with hot water, (2) baking soda and vinegar, (3) a plunger, (4) unscrew and clean the U-bend under the sink, (5) a drain snake for deeper blockages. Call a professional (typically Β£80–£150) if several drains back up at once, sewage smells appear, the blockage is in an outside manhole, or nothing works.

DIY Methods, Gentlest First

1

Boiling water (for grease in kitchen drains)

For a slow kitchen sink caused by fat and grease, pour a kettle of just-boiled water slowly down the drain in two or three stages. Do not use boiling water on PVC waste pipes or porcelain that could crack β€” let it cool slightly first. This melts soft grease blockages and is the gentlest thing to try first.

2

Baking soda and vinegar

Pour about half a cup of baking soda down the drain, followed by half a cup of white vinegar. The fizzing reaction helps break down organic gunk. Cover the plughole, leave for 15–30 minutes, then flush with hot water. Cheap, non-toxic, and surprisingly effective on minor build-up.

3

A plunger

For sinks, baths, and toilets, a plunger creates suction that shifts the blockage. Block any overflow with a wet cloth first to maintain the seal, add enough water to cover the plunger cup, then plunge firmly and repeatedly. A dedicated toilet (flange) plunger works far better on toilets than a flat cup plunger.

4

Clear the U-bend (sink trap)

Place a bucket under the trap, unscrew the U-bend by hand or with grips, and clear out the trapped debris β€” this is the most common blockage point for sinks. Reassemble, ensuring the seals are seated, and run water to check. A 20-minute job that often solves the problem completely.

5

A drain snake or auger

For blockages deeper in the pipe, a flexible drain snake (drain rods for outside drains) reaches in to break up or pull out the obstruction. Feed it in gently, twist to hook the blockage, and withdraw. Avoid forcing it, which can damage the pipe.

When to Stop and Call a Professional

Some signs point to a deeper problem that DIY will not fix β€” and pushing harder can make it worse:

  • Several drains (sink, bath, toilet) back up at the same time β€” likely a blocked main line.
  • Sewage smells, or waste water backing up into the bath or shower when you flush the toilet.
  • The blockage is in an external drain or manhole.
  • You suspect tree roots, collapsed pipe, or repeated blockages in the same spot.
  • Gurgling sounds and slow drainage across the whole house.

In these cases a professional uses high-pressure water jetting and, if needed, a CCTV drain survey to find the underlying cause β€” far beyond what a plunger can reach.

How to Keep Drains Clear

Never pour fat or oil down the sink. It solidifies in the pipe and is the number-one cause of kitchen blockages. Let it cool and bin it.

Use drain strainers. Catch hair in the bathroom and food scraps in the kitchen before they reach the pipe.

Only flush the "three Ps". Pee, paper, and poo. Wet wipes β€” even "flushable" ones β€” and sanitary products are a leading cause of serious blockages.

Flush drains weekly. A kettle of hot water down the kitchen drain once a week keeps grease moving.

Frequently Asked Questions

How do I unblock a drain myself?

Try the gentlest method first: flush with hot (not boiling on plastic) water, then baking soda and vinegar, then a plunger. For sinks, unscrew and clean the U-bend under the trap. For deeper blockages, use a drain snake. If water still will not drain, or multiple drains back up at once, stop and call a professional.

Should I use chemical drain cleaner?

Use it sparingly and only as a last resort. Caustic chemical cleaners can damage older pipes and seals, are dangerous to handle, and do nothing for solid blockages like wet wipes or tree roots. Mechanical methods (plunger, snake, clearing the trap) are safer and usually more effective.

How much does it cost to unblock a drain?

Professional drain unblocking in the UK typically costs Β£80–£150 for a straightforward internal blockage. Severe blockages requiring high-pressure jetting, or a CCTV drain survey to find the cause, cost more β€” often Β£150–£300+. Get the callout fee and likely cost confirmed before the engineer travels.

When should I call a professional for a blocked drain?

Call a pro if multiple drains back up together (a sign of a main-line blockage), if sewage smells or backs up into the house, if the blockage is in an external manhole, or if DIY methods have not worked. These point to a deeper problem that may need jetting or a drain survey.

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