Most blocked drains are cleared by physically dislodging or breaking up the obstruction — usually with drain rods for accessible blockages or high-pressure water jetting for stubborn ones. The right method depends on what is blocking the pipe and where the blockage sits, which is why a brief inspection comes before any clearing work. A simple build-up of grease or wipes can be shifted in minutes; a collapsed pipe is a different problem entirely. This guide explains how the two are told apart and what the common interventions actually do.
What causes a blocked drain?
Drains block when something solid, fibrous or fatty accumulates faster than water can carry it away. Inside the home, the usual culprits are fats and cooking oil that cool and harden, wet wipes (which do not break down like toilet paper), hair, and a slow build-up of soap scum in bathroom waste pipes. Outside, the underground pipes that carry waste to the sewer or septic tank face a different set of problems: tree roots searching for moisture, silt and grit washing in, and debris collecting at bends or joints.
Where the blockage forms tells you a lot. A single slow sink usually means a local problem in that fixture's trap or waste pipe. When several appliances back up at once — say the toilet, bath and basin together — the obstruction is more likely in a shared underground run or the soil stack, the main vertical pipe that carries waste down from upstairs and vents the system. A blocked soil stack can cause gurgling, slow draining across the property, and sometimes smells.
Seasonal factors play a part too. Heavy rain can overwhelm shared drainage and push water back up gullies, while autumn leaves and root growth are more troublesome at certain times of year. Older properties with clay pipework are more prone to root ingress and pipe damage than newer plastic systems.
How a blockage is diagnosed
The right method depends on what is blocking the pipe and where the blockage sits, which is why a brief inspection comes before any clearing work.
Diagnosis starts with the symptoms and a look at the accessible parts of the system. Lifting the inspection chamber covers — the manholes that sit over pipe junctions — shows whether the chambers are running clear or holding water. If one chamber is full and the next is empty, the blockage sits in the pipe between them. This narrows the location quickly and avoids guesswork about which length of pipe is affected.
Standing water that drains away slowly points to a partial blockage; water that does not move at all suggests a full obstruction or a structural fault. Recurring blockages in the same spot are a warning sign. A pipe that clears and then blocks again within weeks often has an underlying cause — a displaced joint, a sag holding water, or roots that keep regrowing — that surface clearing will not fix.
For anything beyond a straightforward clearance, a camera inspection gives a definite answer rather than an educated guess. It confirms not just that a pipe is blocked, but why, and whether the pipe itself is sound.
Rodding, jetting and CCTV surveys
These three methods cover most of the work involved in clearing and assessing drains. They are often used together: clear first, then inspect to check the cause.
- Drain rodding uses flexible rods screwed together and pushed through an access point to physically break up or push out a blockage. It is the simplest and cheapest approach, well suited to soft obstructions in reasonably straight runs. Rodding has limits: it can struggle with hardened grease, compacted debris or blockages a long way from any access point, and it clears the channel rather than scouring the pipe walls clean.
- High-pressure jetting sends water through a hose with a specialised nozzle at high pressure. The jets cut through grease, silt and root masses and scour the inside of the pipe, which is why it deals with build-up that rodding leaves behind. Jetting is effective on longer runs and around bends, though the pressure must be matched to the pipe's condition — very high pressure on already-damaged or fragile pipework can make things worse.
- A CCTV drain survey sends a small waterproof camera along the pipe so its condition can be seen on a screen and recorded. This is the tool that turns guesswork into evidence. It reveals cracks, root intrusion, displaced joints, sags where water collects, and the exact distance to any defect. A survey is commonly carried out after jetting, both to confirm the blockage is gone and to check whether the pipe needs repair.
Surveys are also requested for reasons unconnected to a current blockage — most often before buying a property, or to settle a dispute over which party is responsible for a shared drain. The recording produced is useful documentation in either case.
When a blockage means a broken drain
Sometimes a blockage is the symptom, not the problem. If a drain keeps clogging despite repeated clearing, the pipe itself may be damaged, and clearing it will only ever offer a temporary fix.
Common structural faults include:
- Cracked or fractured pipes, which let soil and roots enter and catch passing waste.
- Displaced or open joints, where sections have shifted apart, creating a ledge that snags debris.
- Sagging or "bellied" pipes, where a length has dropped and holds standing water that silt settles into.
- Root ingress, where roots have grown through a joint or crack and form a mesh that traps everything flowing past.
- Collapsed sections, where the pipe has partially or fully given way, often in older clay drainage.
Signs that point toward a structural fault rather than a simple blockage include blockages that return quickly in the same place, persistent foul smells, patches of lush or sunken ground over the line of a drain, and damp or staining where a soil stack runs inside the building. A CCTV survey confirms whether any of these are present and how serious they are.
Where a defect is found, the options range from localised repair to relining the pipe (fitting a new lining inside the existing one) or excavating and replacing a section. Which is appropriate depends on the type and location of the fault. It is also worth knowing who is responsible: many drains beyond a property's boundary, and those shared between several homes, are the responsibility of the local water company rather than the individual householder. Establishing ownership before commissioning repair work can avoid paying for something that is not yours to fix.
The practical takeaway is straightforward. A one-off blockage from grease or wipes is usually a quick job. A blockage that keeps coming back is a signal to look deeper — and that is where a camera, rather than another round of rodding, earns its keep.