How to unblock a blocked sewer pipe (step by step)

The short answer

Find the inspection chambers either side of the blockage. Rod from the full chamber towards the empty one, so you push the blockage on with the flow of water. However, switch to high-pressure jetting if rodding does not shift it. If the same pipe blocks again within weeks or months, stop rodding and book a CCTV survey. In older North London clay drains, a repeat blockage often means a cracked or displaced pipe, not a fresh obstruction. For anything beyond a plain clear, emergency drain unblocking or a full drain clearance visit is the safer route.

Safety first: this is sewage, not a kitchen sink

A blocked sewer pipe means working near raw sewage, because it carries bacteria, viruses and gases such as hydrogen sulphide. Before you open any chamber cover, wear heavy-duty rubber or nitrile gloves and eye protection. Wear old clothes you are happy to throw away.

Keep your face away from an open chamber. A strong rotten-egg smell is hydrogen sulphide. Therefore, step back and let the air clear. Wash thoroughly afterwards. Do not take anything you touched near the chamber into a food area until it is clean.

If you have a cut on your hands, cover it properly or skip the DIY attempt, since sewage can cause infection through broken skin.

Locating the chambers and rodding

In many North London Victorian terraces, the inspection chamber is a metal or concrete cover set into the front garden, drive or a rear passage. It often sits closer to the boundary than people expect. If you cannot find it, check whether the drain runs to the front or the back of the house. Then look for a slight dip or a cover along that line.

Lift the cover and look inside. A chamber full of water sits upstream of the blockage. An empty one sits beyond it. The blockage lies between the two. Rod from the full chamber towards the empty one, so you push the obstruction on with the flow. Never push it back towards the house.

Feed a flexible drain rod in and turn it clockwise as you advance. Never turn it anticlockwise, because the sections can unscrew and stay in the pipe. When you meet resistance, use a firm push and pull rather than brute force. After a few attempts, run water through and check whether it flows freely.

When rodding is not enough: jetting and CCTV

If rodding fails after a couple of real attempts, the blockage is probably too solid or too far along. Roots, scale or packed debris are the usual causes. High-pressure jetting takes over here. It scours the whole wall of the pipe, not just a hole through the middle. As a result, it clears more thoroughly and is less likely to leave a partial obstruction that blocks again within days. Our complete guide to clearing a blocked drain sets out the full order of methods, and a shorter piece covers clearing blocked drains.

If the blockage returns even after proper jetting, it is still probably structural. Older clay drains in North London are prone to roots at the joints. Some also have displaced or oval sections after decades of ground movement. Why drains block so often in North London explains the causes, and what older clay drains need in Edgware gives a local example. A CCTV survey sends a camera through the pipe, so you see the fault instead of guessing from symptoms.

Before you spend money, check that the pipe is yours. Most shared drains and private sewers outside the boundary have belonged to the water company since 1 October 2011. Our article on who is responsible for blocked drains outside explains how to tell. We have no call-out fee, and we confirm the cost of jetting or a survey through the online enquiry form once we know what is involved.

Related blockages

Not every sewage problem starts at the main drain. For example, for a blocked toilet, try the best way to unblock a toilet without a plumber first. If several fixtures back up together, read a blocked drain pipe, branch or main run. A sewage drain has its own tips, and how to unblock a sewage drain goes through them. If a Saniflo is involved, see why it stops flushing. To cut the risk of repeats, read how often you should have your drains cleaned.

We work across the area, so you can read about drain unblocking in Enfield, blocked drains in Barnet and drain clearance in Edgware. Our blocked drains page covers the full service.

Frequently asked questions

Can I unblock a sewer pipe myself? For a simple blockage, many people manage it, although you need an accessible chamber, the right rodding method and proper protection. It stops being sensible DIY when the blockage returns, when you cannot reach the chamber safely or when the fault looks structural.

How do I clear a blocked sewer pipe outside my house? Find the chamber nearest the blockage. Rod from the full chamber towards the empty one, with the flow. If that fails, jetting reaches further and works more thoroughly than a hand rod.

What is the difference between rodding and jetting? Rodding pushes through a blockage with a rod, and it works for simple obstructions within reach. In contrast, jetting uses high-pressure water to scour the whole pipe wall. It clears more fully and reaches further, but it needs proper equipment.

When should I stop and call someone? Stop if two or three real attempts fail, if water backs up into the property or if the pipe blocks twice in a short time. A repeat blockage usually means something structural. That needs a camera, not a rod. For an urgent case, send the online enquiry form and say so, because we offer 24/7 emergency call-out.