How to Unblock a Blocked Drain (And When It's Time to Call a Plumber)
The quickest way to unblock most household drains is boiling water with a squeeze of washing-up liquid poured down in stages, followed by a proper plunger if that doesn't clear it — both take under ten minutes and deal with the two most common causes: grease and soap-fat build-up. If neither works after two attempts, you're likely dealing with something further down the pipe than a plunger or kettle can reach, and it's time to move on to mechanical clearance rather than repeating the same fix.
Here's the full process in the order we'd actually work through it on a job, plus how to tell early on whether it's even your drain to fix.
What's Actually Causing the Blockage
Before reaching for anything, it helps to know what you're dealing with:
Grease and fat (FOG) — the single most common cause of kitchen sink blockages. Fat that goes down warm sets hard as it cools further along the pipe, narrowing it over time.
Hair and soap scum — the equivalent problem for bathroom sinks, baths and showers.
Wet wipes, cotton buds and sanitary products — the leading cause of toilet blockages beyond the toilet itself, because none of them break down the way toilet paper does.
Food waste — bits that miss the sink strainer, especially rice, pasta and coffee grounds, which expand or clump.
Leaves and debris in an outside gully — very common on UK properties and often mistaken for an internal pipe blockage when it's actually the external grid over the drain that's clogged.
Tree roots — for older external drains, roots can work their way into pipe joints over years, which is a structural issue rather than something you can clear with a plunger.
A collapsed, cracked or sagging section of pipe — the least common cause but the one that explains why a drain blocks again and again despite repeated clearing.
Whose Drain Is It, Anyway?
This matters more than most guides let on, because it decides whether you need a plumber at all.
If the blocked pipe serves only your property — the sink trap, the pipe under your bath, the section running to your own boundary — that's yours to sort out, and a plumber is the right call. But once a drain serves more than one property or connects to the public sewer, responsibility usually shifts to the sewerage company, not you or your plumber.
In the Portsmouth area, this trips people up because there are two separate water companies involved: Portsmouth Water supplies clean drinking water, but it's Southern Water that manages wastewater and sewers across the area. If you've got a blockage that's affecting more than one property, or it's clearly on the public side of the system, that's a job to report to Southern Water directly, not something to pay a plumber to clear.
A quick way to tell which you're dealing with: if only your household is affected and the blockage is inside your boundary, it's a private drain. If neighbours are affected too, or the smell/backup is coming from a manhole or gully outside your boundary line, it's more likely shared or public.
DIY Methods That Actually Work (In the Right Order)
1. Boiling water + washing-up liquid — for kitchen sinks specifically. Squeeze a generous amount of washing-up liquid into the plughole, follow with a kettle of just-boiled water poured in two or three stages, leaving a minute or two between pours. This softens and breaks down grease. Don't use this method on a fully blocked pipe with standing water already sitting in it — the water has nowhere to go and you'll just scald yourself pouring it into a full basin.
2. A proper plunger, used properly — works on sinks, baths, showers and toilets, but the technique matters. Block any overflow hole with a wet cloth first (otherwise you lose suction through it), make sure there's enough water in the basin to cover the plunger cup, and push down gently before pulling up sharply — the pull is what shifts the blockage, not the push.
3. Baking soda and vinegar — half a cup of bicarbonate of soda followed by half a cup of vinegar, left for 20–30 minutes under a plug, then flushed with hot water. It's mild and won't damage pipes, but it's also the weakest option on this list — treat it as a first try for a minor, recent blockage rather than a fix for anything stubborn.
4. A drain snake or flexible wire — feed it down the pipe, rotating as you go, until you feel resistance, then work it through rather than forcing it. This reaches further than a plunger and physically breaks up or hooks out the blockage rather than just dislodging it.
5. Check the external gully first — before assuming it's an internal pipe issue, clear any leaves, silt or debris sitting in the grid over an outside drain. This is a genuinely common cause that gets missed because people go straight to the kitchen sink.
What we'd steer you away from: repeated use of caustic chemical drain unblockers. They can shift a mild blockage, but used repeatedly on the same recurring problem they degrade rubber washers and seals and can damage older pipework — which turns a £0 DIY attempt into a job that now needs a plumber for two things instead of one. If a chemical unblocker hasn't worked after one attempt, that's a sign the blockage needs mechanical clearance, not a second dose.
When DIY Doesn't Work — What That Tells You
If none of the above clears it, the blockage is usually further down the system than household tools can reach, or it's not a simple soft blockage at all. Signs it's moved beyond a DIY job:
More than one fixture is affected at once (e.g. the toilet gurgles when you run the kitchen tap)
Water is backing up at the lowest point in the house — often the bath or a downstairs toilet — rather than just the fixture you're using
There's a smell of sewage rather than just standing water
The same blockage keeps coming back within weeks of clearing it
Any of these point to something in the main run of pipework, not a single trap — which is where professional tools come in.
How Does a Plumber Clear a Blocked Drain?
The process is usually rods first, then escalate if needed:
Drain rods — flexible rods screwed together and pushed through the pipe to physically break up or push through the blockage. This is the starting point for most accessible blockages and clears the majority of jobs without needing anything more.
A powered drain auger/snake — for tougher or more compacted blockages that rods alone won't shift, particularly further along a run of pipe.
High-pressure water jetting — used where the blockage is heavy grease/scale build-up along a length of pipe rather than a single clog; the jet cuts through and flushes the debris out ahead of it rather than just pushing it further down.
A CCTV drain survey — brought in when a blockage keeps recurring despite clearing, or when rodding suggests something structural (a root, a collapsed section, a misaligned joint). A camera run down the pipe shows exactly what's there before anyone recommends further work, rather than guessing.
A competent plumber won't reach for the most expensive tool first — most callouts are solved with rods alone. Jetting and CCTV surveys are for the cases where that genuinely isn't enough, not a default upsell.
What Is the Quickest Way to Unblock a Drain?
For most kitchen and bathroom blockages, boiling water with washing-up liquid or a correctly used plunger clears it within minutes — these deal with the two most common causes (grease and soap/hair build-up) without any tools or call-out required. The "quickest" fix and the "right" fix are usually the same thing for a fresh, single-fixture blockage; it's only once that doesn't work, or the blockage keeps returning, that speed stops being the priority and correctly diagnosing the cause becomes more important than trying another quick fix.
How Much Do Plumbers Charge to Unblock Drains?
National UK pricing guides put a standard call-out in the region of £60, with drain rodding typically landing somewhere between £75–£150, and jetting (needed less often, for heavier or longer-run blockages) more like £120–£250. A CCTV survey, where one's actually needed, tends to add a further £150–£300. Treat these as a rough national picture rather than a quote — actual pricing depends on access, how far into the run the blockage sits, and whether it turns out to be a five-minute rodding job or something that needs a repeat visit.
What we can tell you about how we quote: you'll be told the cost before any work starts, and if it turns out to be a straightforward rodding job rather than something bigger, that's what you're charged for — not a flat "drain callout" rate regardless of what was actually involved.
Common Mistakes We See
The most common one is reaching for a chemical drain unblocker two or three times in a row on a blockage that isn't clearing, rather than stopping after the first attempt and trying rods or calling someone. It rarely works better the second or third time, and it's the fastest way to turn a simple clog into a damaged seal or a pipe that now needs replacing as well as clearing.
The second is assuming a recurring blockage is "just bad luck" rather than a sign of a structural issue further down the line. A drain that blocks every few months in the same spot is telling you something specific — usually root ingress or a section that's starting to sag — and it's worth a CCTV look before it becomes an emergency.
Preventing Blocked Drains
Fit a cheap hair/food strainer over sink and shower plugholes
Never pour fat or cooking oil down the sink — let it cool and bin it
Only flush toilet paper — wipes, cotton buds and sanitary products go in the bin even if labelled "flushable"
Clear leaves and debris from external gullies a couple of times a year, especially in autumn
If a property has a history of recurring blockages, a one-off CCTV survey is cheaper in the long run than repeated emergency call-outs for the same spot
When to Call a Plumber
Call a professional if:
Two DIY attempts (a different method each time) haven't cleared it
More than one fixture is affected, or you're getting backup at the lowest point in the house
There's a smell of sewage, standing water that won't drain at all, or it's happened before in the same spot
You've confirmed it's a private drain, not a shared/public one Southern Water needs to handle
If that's where you've landed, this is routine work for our Portsmouth plumbing team — Gas Safe and MCS registered, with Duncan Vella and Rhys Browne handling jobs directly rather than a call centre passing you between operators, and a fixed cost you're told before anything starts. You can see the full range of what we cover on our plumbing services page.
If that's where you've landed, this is routine work for our Portsmouth plumbing team — Gas Safe and MCS registered, with Duncan Vella handling jobs directly rather than a call centre passing you between operators, and a fixed cost you're told before anything starts. Call 07501 016990 or request a free quote, and we'll get someone out to sort it — see the full range of what we cover on our plumbing services page.
FAQs
Is a blocked drain a plumbing emergency?
Not usually, unless sewage is backing up into the house, multiple fixtures are affected at once, or it's causing standing water somewhere it shouldn't be. A single slow-draining sink can typically wait for a normal appointment.
Can a blocked drain cause damage if it's left?
Yes — a blockage that isn't dealt with can lead to water backing up and overflowing at the lowest connected point, which risks damage to flooring, cabinetry or a ceiling below if it's an upstairs fixture. Recurring blockages left unaddressed can also mean an existing crack or root ingress gets worse over time.
Will a plumber unblock a drain, or do I need Southern Water?
If it's a private drain serving only your property, a plumber handles it. If it's shared with neighbouring properties or connects to the public sewer, that's Southern Water's responsibility to fix, not something you should be paying a plumber for.
Do drain unblocking chemicals damage pipes?
Used occasionally, most shouldn't cause harm. Used repeatedly on a blockage that isn't clearing, they can degrade rubber seals and washers and, on older pipework, the pipe material itself — which is why we'd suggest stopping after one attempt rather than reaching for a second bottle.
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