How to Clear a Blocked Outside Drain
Always wear rubber gloves and eye protection when working on drains. Drain water can contain harmful bacteria. Do not enter any drain chamber — they may contain toxic gases.
A blocked outside drain is usually caused by leaves, debris, fat deposits, or a build-up of sediment in the inspection chamber. It is one of the more unpleasant DIY jobs but is very achievable with drain rods, which can be hired from most tool hire companies for around £20–30/day.
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Most likely cause & what to check
Lift the drain cover using a drain cover key or flat bar. Drain covers are heavy — have a helper or use a proper drain lifter. Inspect the chamber — if it is full of water, the blockage is downstream; if it is empty, the blockage is upstream.
If the chamber is empty, move to the next chamber upstream and inspect. Repeat until you find the chamber where water is backed up — the blockage is between that chamber and the next one downstream.
Assemble drain rods — screw together 1–2 metre sections and fit either a rubber plunger attachment or a corkscrew (worm) attachment. A corkscrew is better for breaking up solid blockages; a plunger for pushing debris through.
Insert the rods into the full chamber and push them toward the downstream chamber (in the direction of flow). Always twist rods clockwise while pushing — never anti-clockwise or the sections will unscrew and stay in the drain.
Work the rods back and forth while twisting. You will feel resistance when you hit the blockage — keep working until you feel the rods push through. A sudden rush of water and drop in level confirms the blockage is clear.
Once clear, flush through with a garden hose for 5–10 minutes to wash remaining debris downstream. Pour a bucket of hot water mixed with drain cleaner through to dissolve any grease.
If you cannot clear the blockage with rods, the drain may have a root ingress, collapsed section, or a displaced joint — a drainage company with a CCTV camera can diagnose this (£80–200 for a CCTV survey).
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