A blocked drain is usually cleared by locating the obstruction, then either plunging it, rodding it loose, or breaking it down with high-pressure water. Most household blockages sit in an accessible spot and respond to simple methods. The harder part is working out where the blockage lies before you reach for a tool — that single step saves time and stops you treating the wrong section of pipe.
This guide explains how to read the early signs, where blockages tend to gather, the methods used to shift them, and the point at which a camera survey starts to earn its place.
First signs a drain is blocking up
Drains rarely fail all at once. They give warning, and catching the signs early often means a quick clear rather than a flooded yard.
- Slow draining — a sink, bath or basin that empties more sluggishly than it used to. A partial blockage is narrowing the pipe.
- Gurgling sounds — air being pulled past a building obstruction as water tries to get through, often heard at a plughole or toilet after another fixture is used.
- Smells — stale or sewage odours rising from a plughole or an outside drain suggest waste is sitting still rather than flowing away.
- Water rising elsewhere — flush the toilet and the shower tray fills, or use the washing machine and an outside gully overflows. That points to a shared blockage downstream of both fixtures.
- Standing water at an outside drain — a gully or inspection chamber holding water that should have drained away.
One slow fixture usually means a local problem. Several fixtures misbehaving together points further down the system, towards a shared pipe or the main drain run.
Where the blockage usually sits: inside or out
A blocked drain is usually cleared by locating the obstruction, then either plunging it, rodding it loose, or breaking it down with high-pressure water.
Knowing whether the trouble is inside the property or beyond the wall tells you which method is likely to work and who is responsible for it.
Inside, blockages collect in the traps under sinks and baths — the U-bend that holds a water seal — and in short waste pipes. These are the easiest to reach. Fat, soap, hair and food debris are the usual culprits. A toilet that backs up on its own, while other fixtures run fine, often has a blockage close to the pan.
Outside, waste from the building gathers in a few key places:
- The soil stack — the large vertical pipe, usually running up an outside wall, that carries waste from toilets and upper-floor fixtures down to the underground drain. A blockage here affects everything above it.
- The gully and gully trap — a gully is the open drain at ground level that takes water from sinks, washing machines and surface run-off. The gully trap is the water-filled bend beneath it. Leaves, grease and grit build up here and are simple to clear by hand.
- Inspection chambers — the access points (sometimes called manholes) where underground pipes meet. Lifting the cover shows whether water is flowing through or pooling, which helps pinpoint the blocked section.
If a chamber near the boundary is full but the one closer to the house is clear, the blockage sits between them. In England and Wales, pipes shared with neighbours or running beyond the property boundary are often the water company's responsibility rather than the householder's, so it is worth checking before arranging private work.
Clearing methods, from plunging to high-pressure jetting
The right method depends on where the blockage is and what it is made of. Methods run from the simple and cheap to the powered and professional.
Plunging is the first resort for sinks, basins and toilets. A cup plunger creates pressure waves that dislodge soft blockages near the trap. It works best when the blockage is close and not yet solid.
Hand clearing a trap means unscrewing the U-bend under a sink and removing the debris directly. Messy but reliable for hair and grease close to a plughole. Outside, a gully trap can often be scooped clear by hand or with a small trowel.
Drain rods are screw-together flexible rods pushed into a drain through an inspection chamber. Fitted with a plunger or corkscrew head, they reach blockages several metres along underground pipes. A key point: rods should be turned clockwise as they go, so the sections do not unscrew and leave a head stuck in the pipe.
High-pressure jetting uses a hose that fires water through a nozzle at high pressure, scouring the pipe walls and flushing debris downstream. It handles grease, scale and compacted matter that rods only push around, and it cleans the full bore of the pipe rather than punching a hole through the blockage. Jetting is a powered method, normally carried out by a drainage firm with the right equipment, and it is the go-to for stubborn or recurring blockages.
Chemical drain cleaners are sometimes used on soft organic blockages, but they are caustic, can damage older pipework and do little against roots or solid matter. They are best treated as a limited option rather than a first choice.
When a CCTV survey is worth it
A CCTV drain survey sends a small waterproof camera along the pipe on a flexible rod, sending live pictures back so the inside of the drain can be seen. It answers the question that rodding and jetting cannot: not just where the blockage is, but why it keeps happening.
It earns its keep in a few situations:
- Repeat blockages — when a drain clears and blocks again within weeks, something structural is usually behind it: a collapsed section, a dip that traps debris, or tree roots growing through a joint.
- Before buying a property — a survey shows the condition of underground drains that no other inspection reveals, which can matter where the pipes are old.
- Disputes over responsibility — footage locates a problem precisely and shows which side of a boundary it falls on, useful when liability is shared.
- Planning building work — knowing where drains run prevents an extension being built over a pipe that later fails.
For a one-off blockage that clears cleanly and stays clear, a survey is rarely needed. Its value comes when a blockage signals an underlying fault, so paying to look once can prevent paying to clear the same drain repeatedly. A good survey produces a recorded copy and a report, so the findings can be checked against any quote for repairs.