What you get

A video walk-through of the drainage system, plus a written report identifying material, condition, defects, joints, blockages and roots.

When to do one

Before an extension that is anywhere near drainage. Before a build-over application. After buying a property where the survey flagged drainage uncertainty.

What to ask for

A report that locates each feature on a plan, not just a video clip with vague descriptions. You want manhole-to-manhole runs, depths, and a clear summary of defects.