A blocked drain happens when something stops water flowing freely through the pipes that carry waste away from a property. Most domestic blockages are caused by a build-up of grease, hair, wet wipes or food waste, and many can be cleared with simple tools — but a recurring blockage usually points to a fault in the drainage system itself, which is the network of pipes and chambers that moves wastewater from sinks, toilets and gutters to the public sewer.
What causes a blocked drain?
The cause depends largely on where the blockage sits. Inside the house, kitchen and bathroom waste pipes (the smaller pipes under sinks, baths and basins) tend to clog with fat, soap scum, hair and the residue from cleaning products. Toilets block when wet wipes, sanitary items, nappies or too much paper are flushed — even wipes labelled "flushable" do not break down the way toilet paper does.
Outside, the larger soil pipes (which carry toilet waste) and the underground drains can be obstructed for different reasons. Tree and shrub roots are a common culprit: they seek out moisture and work into pipe joints, gradually filling the bore. Other causes include collapsed or cracked sections, displaced joints where the ground has shifted, scale and debris that settle over time, and silt washed in from gardens or damaged gullies. Older clay and pitch-fibre pipes are especially prone to root intrusion and deformation.
A few warning signs tend to appear before a full blockage. Water draining slowly, gurgling sounds from plugholes, an unpleasant smell near a gully or manhole, and waste backing up at the lowest fitting in the house all suggest a partial obstruction that is worth investigating early.
Clearing blockages versus treating the cause
A blocked drain happens when something stops water flowing freely through the pipes that carry waste away from a property.
Clearing a blockage and fixing what caused it are two different jobs. Clearing restores flow; treating the cause stops the problem returning. A plunger, a hand auger (a flexible rod with a coiled end, sometimes called a drain snake) or hot water and washing-up liquid will shift many minor blockages in waste pipes. Caustic chemical cleaners can work on grease and hair but should be used carefully — they can damage older pipes and seals, and they do nothing for roots or structural faults.
For blockages further down the system, a contractor will often use drain rods (screw-together rods pushed through an open chamber) or high-pressure water jetting, which scours the inside of the pipe with a fine jet. Jetting is effective at removing grease, scale and fine roots and is gentler on most pipework than mechanical cutting.
The key distinction is whether the blockage is a one-off or a symptom. A single clog from a build-up of fat may never recur once cleared and once habits change. A blockage that returns within weeks, or that affects several fittings at once, is rarely solved by clearing alone. In those cases the sensible next step is to find out what is happening inside the pipe rather than repeatedly clearing the same fault.
When a CCTV drain survey is worthwhile
A CCTV drain survey is worth considering when a blockage keeps coming back, when the cause is not obvious, or before buying a property with older drainage. The survey involves feeding a small waterproof camera through the pipes to record their condition. It shows exactly where a problem lies and what type it is — roots, a crack, a collapse, a dip that holds water, or simply a build-up of debris.
This matters because it removes guesswork. Without a camera, repeated clearing can become an expensive cycle that never addresses the underlying fault. A survey produces footage and often a written report with the location and depth of any defect, which is useful for planning a repair and for sharing with an insurer or a managing agent where one is involved.
A manhole inspection usually goes hand in hand with this. Lifting the chamber covers lets the inspector see the flow, check the condition of the open channels in the base of each chamber, and identify which run of pipe to survey. For homebuyers, a survey can reveal liability and likely future cost before contracts are exchanged. It is also commonly requested where there are signs of subsidence, persistent damp, or unexplained smells.
It is worth checking who is responsible for a given length of pipe before commissioning work. In England and Wales, many shared and lateral drains transferred to the local water company in 2011, so some underground problems may fall to the sewerage provider rather than the homeowner. The boundary of the property and the position of the public sewer determine where that responsibility sits.
Repairs, relining and collapsed sections
When a survey shows a structural fault, the repair depends on the damage. Minor cracks and open joints can sometimes be sealed in place. More extensive damage often calls for relining, where a resin-soaked liner is inserted into the existing pipe and cured to form a new pipe within the old one. This is a "no-dig" method that avoids excavation and can be carried out through existing access points, which makes it less disruptive than digging up a drive or garden.
A patch repair fixes a short defect, while a full liner renews a longer run. Both rely on the host pipe being broadly intact and the right shape, so relining is not suitable where a pipe has badly collapsed or lost its line. In those cases, excavation and replacement of the affected section is usually the only durable answer. Roots that have entered through a joint are typically cut out first, after which the joint may be relined or replaced to stop regrowth.
Whatever method is used, a follow-up camera survey is the normal way to confirm the repair has worked and that the flow is clear. Good practice is to ask a contractor to explain why a particular repair has been recommended, to see the survey footage that supports it, and to compare the cost and lifespan of relining against excavation before deciding. Keeping the report on file also helps if the same stretch of pipe gives trouble again in future.