How to clear a blocked manhole: a step-by-step guide

A manhole full of standing water tells you a blockage exists downstream of that chamber. Working out which chamber to lift, and in what order, is most of the job — the clearance itself is often the quick part.

Safety before anything else

• Wear gloves and eye protection; wash thoroughly afterwards
• Never enter a chamber — confined space entry needs gas monitoring and trained personnel
• Use proper keys to lift a cover, lift with your legs, and never leave an open chamber unattended
• Keep children and pets well away, and cone or barrier the area on driveways and car parks
• Do not lift covers on a live highway — that is a job for a contractor with traffic management

Step 1 — find the blockage by working downstream

1. 1Lift the chamber closest to the property and note whether it holds standing water.
2. 2Move to the next chamber downstream and check again.
3. 3Keep going until you find a chamber that is empty and flowing normally.
4. 4The blockage is in the run between the last full chamber and the first empty one.

If every chamber on your property is full right down to the boundary, the problem may be in the public sewer or a shared lateral — worth confirming before you spend money, and worth checking whether neighbours are affected too.

Step 2 — try rodding

Screw rods together tightly and feed them into the outlet of the last full chamber, turning clockwise only — turning anticlockwise unscrews the rods and leaves them in the drain. Use a plunger or worm head for soft blockages. Push and rotate rather than ramming; you are trying to open a channel through the blockage so flow can start eroding it.

Step 3 — when rodding is not enough

Rodding punches a hole through a blockage. High-pressure water jetting scours the full bore of the pipe and flushes debris away, which is why jetting is the proper fix for fat, silt, scale and root mats. A jetting unit with the correct nozzle can clear a run in minutes that rods will only ever partially open.

• Fat and grease build-up — jetting with a degreasing nozzle
• Silt and sand in a shallow-fall run — jetting plus chamber clearance
• Root ingress — root-cutting head, then CCTV to find the entry point
• Collapsed or displaced pipe — no amount of jetting will fix it; a survey and repair are needed

Step 4 — find out why it blocked

One blockage is bad luck. A second in the same run is a defect. A CCTV survey after clearance shows whether you are dealing with a usage problem, a fall problem or physical damage, and gives you a report you can use with insurers or a managing agent.

What not to do

• Do not tip caustic drain chemicals into a full chamber — they rarely work on silt or roots and make the job hazardous for whoever clears it
• Do not bail effluent onto a lawn, driveway or into a surface water gully
• Do not force rods against solid resistance; you can dislodge a joint
• Do not keep using water heavily while the chamber is full