A camera goes into the pipe, records what is there, and produces a graded report. That is the whole idea. What varies between firms is what you are handed afterwards.
A survey camera is a small waterproof head on a semi-rigid rod, or on a self-driving crawler for larger pipes. It goes in through an existing manhole, a gully, or if there is no other access, the toilet pan. Nothing is dug up and nothing is broken out.
It travels the run recording continuously, with a counter measuring how far in it has gone. That distance is what makes the report usable: a defect is not just 'in the back garden', it is at 7.4 metres from the rear chamber, which is a hole rather than a trench.
Cracks and fractures in clay. Displaced or open joints where the ground has settled. Root ingress, which follows water out of a leaking joint rather than breaking in. Deformation in pitch-fibre, the tar-and-cellulose pipe used across west Warrington in the 1960s and 70s, which flattens rather than cracking. Silt and standing water where a run has lost its fall. Debris left in the line during construction — common on the newer estates here. And connections that go somewhere nobody expected.
Each of those has a different fix and a very different cost, which is why 'the drain is blocked' is not a diagnosis.
You get a two-hour arrival window and the engineer's name. The survey itself is about an hour for a typical house. You do not need to be there for all of it, but most people watch the monitor for the first few minutes because it is more interesting than they expect.
The report and footage arrive the same day. If something needs urgent attention you are told on the doorstep, not in an email three days later.
Worth doing: before you exchange on a house, when a drain has blocked more than once, when there is a smell you cannot place, when the ground has dropped, when you are building over a run, and when an insurer needs evidence.
Not worth doing: a one-off blockage that cleared and has not returned. That is maintenance. We will tell you so on the phone rather than take the booking.