Property How to unblock a sink

Plumbing · Beginner

How to unblock a sink

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Most blocked basins and kitchen sinks are a wad of hair, soap or grease sitting in the trap under the bowl — the U-bend or bottle trap. A plunger, a bucket and a willingness to unscrew that trap will clear a lot of them, without pouring harsh chemicals down first. If several fittings are backing up at once, the problem may be further along the waste, and that is a plumber’s job.

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At a glance

Difficulty

Beginner

Time

20–60 minutes

Rough cost

Often nothing if you already have a plunger and a bucket. A plunger and a pair of gloves are inexpensive — check the current prices. Avoid buying a cupboard full of chemical drain cleaners as your first move.

People

Your call

Go or no?

Fancy giving it a go, or would you rather call in a plumber? There’s no wrong answer.

Right then. Here’s the kit, then the steps.

No problem. We’ll show you how to find a local plumber.

Shop the full kit

You can pick up the items below as you need them. Prices vary by shop and country, so we have not invented a figure here — check the live price before you buy. Shop links go to a product search on a local store for your country. Until a tracking tag is in place they are ordinary store links, not tracking URLs.

All-in-one kit

There is not usually a single boxed kit for this job. Buy the items below as you need them, and skip anything you already have.

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Before you start

Safety

Stop and get a pro: If more than one sink, bath or toilet is backing up, or you see sewage rather than soapy water, stop and call a plumber — that may be a shared or main waste, not a simple U-bend. Do not mix different chemical drain cleaners, and do not plunge after you have used them: the liquid can splash onto your skin or into your face. If you cannot get the water off, or a waste pipe is cracked, call a plumber. This is not a job on the incoming water mains, and not a job on a toilet soil pipe unless you are already sure of what you are doing.

Wear gloves. The water in a trap is dirty. Safety glasses are sensible if you have already used a cleaner, though you should not plunge in that case.
Put a bucket and old towels under the trap before you loosen anything. The trap is full of water, even if the sink looks empty.
Never mix bleach with an acidic or ammonia drain cleaner. If a cleaner is already in the sink, do not add another, and do not put your hands or a plunger in until it has been flushed through and you are sure it is safe.
If you have to go into a tight cupboard, watch for the isolation valves and the electrical connection to a dishwasher or waste disposal — do not pull on cables.
A waste disposal unit, if you have one, should be isolated at the switch and the plug before you put a hand anywhere near it.

Prep that is worth doing

Bail standing water out of the sink into a bucket so you can see what you are doing, and so a plunger has a chance to work.
If there is an overflow, you will need to block it with a damp cloth when you plunge, or the air will go the wrong way.
Clear the cupboard so you have room for a bucket under the trap.

Tools and materials

Check the live price at a shop you trust. Typical prices on this site, where they appear, were checked in the UK and may be out of date. Do not invent or assume a figure from this table. Shop links go to a product search on a local store for your country. Until a tracking tag is in place they are ordinary store links, not tracking URLs.

Item	Why you need it	Typical price
A sink plunger	A small cup plunger is usually enough for a basin or kitchen sink. It needs a seal over the plughole.	check price
A bucket and old towels	To catch the trap water and to protect the cupboard floor.	check price
Rubber gloves	The trap water is unpleasant.	check price
An adjustable spanner or groove-joint pliers (optional)	Some traps have a nut you can do by hand; others are stiffer.	check price
An old wire coat hanger or a plastic drain hair hook (optional)	For pulling a hair clog out of the trap or the tail of the waste.	check price
A cloth to block the overflow	Stops the plunger’s push escaping through the overflow slot.	check price

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Step-by-step

Try a plunger first. If that fails, take the trap off over a bucket, clean it, and only then think about the pipe beyond. Leave chemical cleaners as a last resort, not the first.

Bail the sink and try a plunger
Take out as much standing water as you can, then leave enough for the plunger to sit in. Block the overflow with a damp cloth, and block a second bowl if it is a 1½-bowl sink. Seat the plunger over the plughole and pump firmly and steadily, keeping the seal. Lift off and see whether the water runs. Repeat a few times before you give up.
If it is still blocked, prepare to open the trap
Put a bucket under the U-bend or bottle trap. The trap is the bend or can-shaped section immediately under the sink. Loosen the unions by hand if you can, or with a cloth and a spanner if they are tight. Do not twist the waste pipe in the wall.
Take the trap off and clean it
Lower it into the bucket. Tip out the water and the clog — often a plug of hair and soap, or a lump of kitchen grease and food. Rinse the trap in the bucket. Look up into the waste from the plughole and along the pipe towards the wall, and pull out anything you can reach with a hook. Do not shove a long object deep into the stack.
Refit the trap and run water
Check the washers or plastic olives are seated, hand-tighten the unions, and then a little more if they drip. Put water in the sink and pull the plug. The trap must be left full of water — that water seal is what stops smells coming back. Check under the sink for drips.
If it still does not run
The blockage is further along the waste. You can try a simple hand-wound waste auger in the pipe, gently, if you own one. If several fittings are slow, if water comes back from another fitting, or if you cannot reach the clog, stop and call a plumber. Avoid pouring a chemical cleaner down as a last hopeful step after you have had the trap apart — it rarely helps at that point and makes the next visit nastier.

General guidance only. Check our disclaimer.

Common mistakes

Reaching for chemicals first. They often sit on top of a solid clog, damage the trap, and make plunging dangerous.
Forgetting the overflow. The plunger will not work if the air escapes through the slot at the back of the basin.
Taking the trap off with no bucket. You will remember this only once.
Overtightening plastic trap nuts. They crack, and then you have a leak as well as a blockage.
Pushing the clog further into the pipe. Hook it out; do not ram it towards the stack.
Ignoring a building-wide backup. That is a plumber, or the building’s waste, not more plunging.

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FAQ

Kitchen or bathroom — is the method the same?

Yes. Kitchen clogs are often grease and food; bathroom clogs are often hair and soap. The trap is still the first place to look. Do not pour fat down a clear sink either — it cools and sets further along.

Should I use a chemical drain cleaner?

It is better not to, especially as the first move, and never mixed with another cleaner. If you have already poured some in and it has not worked, do not plunge, and tell a plumber before they open the trap.

The sink smells but it is not blocked.

The trap may have dried out if the sink is rarely used — run water for a few seconds. If the smell remains, the trap washers may be leaking or the waste pipe may be loose. A persistent sewer smell needs a plumber.

Can I use this on a shower tray or a bath?

A plunger can help a bath, with the overflow blocked. Shower wastes are often low and tight. If you cannot get to a trap, or the tray is sealed in, get a plumber rather than forcing a panel.

Would rather not DIY? Find a local plumber

If the blockage is past the trap, if waste is coming back up, or if you would rather not sit under a sink with a bucket, a plumber has rods, a drain camera and a way to get the waste apart without flooding the cupboard.

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