Drainage Training

This video was created for a Subsidence Forum Training Day.

Catalyst’s Head of Technical and Network, Paul Duddle, explains how household drainage systems work, how key faults can develop, and the main techniques available to find and diagnose these faults.

Sewer Coding

Sewer coding is a central element of the CCTV drainage surveying process.

The sewer coding system is used to identify the location and structure of a pipe, and defects it may have. Our video shows how a drainage engineer uses sewer coding during a drain survey.

Drainage pipe defects

There are many ways a drainage pipe can become damaged.

This video shows the common causes of these defects, including pipe cracking and pipe collapses.

Joint displacements

Most drainage pipes are made up of joined-together sections.

A joint displacement occurs where two of these sections come apart. Our video explains the different types of joint displacement commonly found in sewer systems.


Drainage pipes can be damaged by different types of cracks. Our video describes these different cracks.

It also explains how they form and why identifying the type and extent of cracking is often important when selecting the best way to carry out a repair.

Backdrop manholes

Backdrop manholes form an essential element of many domestic and commercial drainage systems.

They allow underground pipes to be stepped down to main sewers so wastewater runs smoothly. This video gives more information about why they are installed and how they work.

What is a gully?

Gullies are an essential element of drainage systems for both commercial and private properties.

This video explains the importance of planned and preventative gully maintenance to prevent blockages and potential subsidence problems.

Gully connections

Gullies are ground-level drains that collect surface water or foul water (or both) and direct the water to connecting underground pipes.

Our video explains why carrying out surveys to establish where water comes from, where it goes is and who is responsible for it, are essential for good drain maintenance.

CAT and sonde

Drainage engineers often have to locate and trace underground pipes.

A quick and accurate way to do this is to use a CAT and sonde, which use radio waves to pinpoint underground locations. Our video shows CAT and sonde technology in action.

Sewer pipe root ingress

Tree and shrub roots can get into sewer pipes, causing serious blockages and making pipe defects worse.

This process is called pipe root ingress. Our video shows the three main types of root ingress: fine root ingress, tap root ingress and root mass.

Water testing

It can often be vitally important to be sure how water drains away after it enters an underground sewer system.

For example, water may be seeping through displaced joints or cracks. Our video shows how carrying out a water drop test can quickly establish if pipes are carrying water properly or are leaking.

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