External drains carry waste and rainwater from your property to the public sewer. They include gullies, manholes, inspection chambers, and the buried pipes between them. Leaves, silt, roots, and grit build up inside them over time. Because the pipes sit underground, problems often show only when water pools in the garden or backs up into the house.
The engineer opens the manholes and chambers to see where the water stops. Water levels and flow direction show where the blockage sits. Because the pipes are out of sight, this step saves a lot of guesswork.
A jetting hose feeds into the blocked section. The jets break up the blockage, while they also scour the pipe walls. Heavy debris may need a second pass.
Where it suits the job, a camera can run through the cleared pipe. For example, it can show roots, cracks, or a displaced joint. Ask whether this costs extra.
The engineer refits the covers and clears any loose debris. Ask for advice on the drain's condition and on any repair it may need. Since roots and cracks can bring a blockage back, this advice is worth having.
The cost of external drain unblocking depends on the pipe length and the type of blockage. Tree roots or packed debris can need longer jetting. Because the cost can change once the engineer sees the drain, ask for a written quote before work starts. Also ask whether there is a call-out charge.
You look after the drain inside your property boundary. In 2011, Yorkshire Water took on many private sewers and the drains that run beyond property boundaries. Since ownership can be hard to judge, check Yorkshire Water's website before you pay for work.
Yes, roots are a common cause of outside blockages. Roots seek out water, so they can enter through cracks or loose joints. However, a camera check can spot them early, before the pipe blocks fully.
There is no fixed rule. Homes with large trees near the pipes, or past blockages, may need checks more often. Since every garden differs, ask the engineer what schedule suits your drains.