Blocked drains: when to DIY and when to call a drainage specialist
A slow-draining sink or a toilet that gurgles after every flush is one of those problems that is easy to ignore right up until it is not. Most minor blockages are genuinely manageable without calling anyone, but a smaller number are a sign of something further down the system that no amount of plunging will fix — knowing which is which saves both money and a nasty surprise.
For a single slow or blocked sink, bath or shower, the simplest first step is usually a plunger — a cup plunger for a flat-bottomed sink, held firmly over the plughole with enough water in the basin to cover the rubber cup, pumped several times rather than once. If that does not clear it, a kettle of hot (not boiling, on plastic pipework) water followed by a couple of tablespoons of bicarbonate of soda and then white vinegar, left for ten to fifteen minutes before flushing through with hot water, can shift a mild build-up of grease or soap scum. It is worth being cautious with shop-bought chemical drain cleaners used repeatedly — they can be harsh on older pipework and are not something to combine with each other or with the vinegar-and-soda approach in the same attempt.
For an outside gully — the grated drain often found near a kitchen or bathroom external wall — clearing leaves, debris and silt out of the grate itself is often enough, since a lot of "blocked drain" calls for outside gullies turn out to be a surface blockage rather than anything in the pipe below.
A handful of signs point toward something beyond a simple DIY fix. If more than one fixture is affected at once — say, the toilet gurgles when the bath empties, or water backs up in the shower when the washing machine drains — that usually means the blockage is further down the shared pipework rather than in any one fitting. A bad smell that does not clear after cleaning, a blockage that comes back within days of being cleared, or water backing up rather than draining slowly, are all reasonable signs to call a professional rather than keep trying the same fix.
This is where a CCTV drain survey earns its cost. A specialist feeds a waterproof camera on a flexible rod into the drain to see exactly what is happening inside — a collapsed section of pipe, roots that have grown into a joint, a misaligned pipe, or a build-up of fat and grease, sometimes substantial enough to be described as a "fatberg." Rather than guessing and jetting the drain repeatedly, a survey identifies the actual cause and location first, which usually makes the eventual fix quicker and sometimes cheaper overall, particularly for a recurring blockage that keeps coming back.
Working out who is actually responsible for fixing a blocked drain — and paying for it — depends on where the blockage is, and this changed significantly in recent years. As a general rule, a drain that runs within your property boundary and serves only your home is your responsibility as the owner. A pipe running from your boundary out to the public sewer, however, including many of the shared "lateral" drains that serve more than one property before joining the main sewer, is now generally the responsibility of the water and sewerage company, not the homeowner.
This is the result of a change that came into effect on 1 October 2011, when private sewers and lateral drains that were already connected to the public sewer network were automatically transferred to statutory water and sewerage companies across England and Wales — described by DEFRA at the time as the biggest change in sewerage responsibility since 1937. Before that date, responsibility for these shared and lateral pipes was often split in complicated ways between neighbouring property owners; since the transfer, the water company is generally responsible for maintaining and repairing them instead, even though the pipe may still run under private land. Because this depends on the exact layout and history of the drain in question, and rules can differ slightly by nation and by water company, it is worth treating this as general background rather than a definitive answer for your specific property — if in doubt, your local water company can usually confirm who is responsible for a particular stretch of pipe, and in some cases will investigate a shared blockage without charge before you commission a private CCTV survey.
A little prevention goes a long way regardless of who is ultimately responsible: keeping fat, oil and food scraps out of kitchen drains, using a simple drain guard over plugholes to catch hair and debris, and sticking to the "three Ps" in the toilet — pee, poo and paper, nothing else, including so-called flushable wipes — heads off a large share of blockages before they start. If you are dealing with a blockage that will not clear, keeps returning, or seems to involve more than one fixture, our directory lists drainage specialists and plumbers covering towns and cities across the UK who can survey and fix it properly.
Frequently asked questions
A plunger is usually the first thing to try, followed by hot water with bicarbonate of soda and vinegar for a mild grease or soap build-up. Repeated use of chemical drain cleaners on older pipework is worth avoiding.
A specialist feeds a waterproof camera into the drain to see exactly what is causing a blockage — such as a collapsed pipe, tree roots, or a fat build-up — so the fix can target the actual cause rather than being a guess.
Generally, a drain within your property boundary serving only your home is your responsibility. Many shared and lateral drains running to the public sewer were transferred to water and sewerage companies in October 2011, so they are often the water company’s responsibility instead — worth confirming with your local water company if you are unsure.
Fat, oil and food scraps down the kitchen sink, and anything other than pee, poo and paper down the toilet, including wipes marketed as flushable — these are common causes of blockages and, further downstream, sewer fatbergs.