How do I clear a blocked outside drain?

Drains run in a chain from the house to the sewer, with inspection chambers at junctions and changes of direction. Because water backs up behind a blockage, checking the chambers in order locates it precisely rather than by guesswork.

Safety

What you'll need

• Drain rods
• Waterproof gloves
• Eye protection
• Bucket (optional)
• Hose (optional)

Step by step

1. Find and lift the inspection chamber covers.Usually near the house, at junctions, and near the boundary. Use a proper lifting key or two screwdrivers in the slots.
2. Check each chamber in sequence from the house outwards.A full chamber means the blockage is downstream of it. An empty one means the blockage is upstream. The transition point is your location.
3. Note whether the boundary chamber is full.If the last chamber before the boundary is also full, the blockage may be in the shared sewer, which is the water company's responsibility and free to clear.
4. Assemble the rods and start in the chamber downstream of the blockage.Rodding with the flow is more effective and pushes debris towards the sewer rather than back towards the house.
5. Always turn the rods clockwise as you push.This is important — turning anti-clockwise unscrews the joints and you lose rods in the drain, which is a much bigger problem.
6. Push and pull rather than just pushing.The plunging action breaks up the blockage. Steady work is more effective than force.
7. Flush thoroughly with a hose once it clears.It carries away the loosened debris rather than letting it settle into the next blockage further along.
8. Work out why it blocked.Fat and wipes are the usual causes. Roots, a collapsed pipe or a displaced joint show as repeated blockages in the same place and need a camera survey.

Tips

• Drain rods are inexpensive to buy and cheap to hire, and considerably cheaper than a call-out.
• Wipes are the single biggest cause of household drain blockages, including ones labelled flushable. Nothing but paper should go down a toilet.
• Repeated blockages in the same spot mean a structural problem — roots, a crack or a fallen joint. A camera survey identifies it and is worth it before paying repeatedly for clearing.

Common mistakes

• Turning rods anti-clockwise — The threaded joints unscrew and rods are left in the drain, turning a blockage into a much more expensive problem.
• Pouring caustic drain cleaner into a standing blockage — It sits in water, achieves little, and creates a hazardous splash risk when you then rod it.
• Not checking the boundary chamber — If the blockage is in the shared sewer, the water company clears it free. Paying a private contractor for that is money wasted.

Questions people ask