A drainage investigation looks for the cause of a problem that keeps coming back. A general survey checks the whole system, while an investigation follows your symptoms and traces them to the source.
It suits repeat blockages, damp patches, bad smells and slow drains that rods do not cure. A camera on a rod or a small crawler follows the pipe and records what it sees. The engineer can then mark where the fault sits, because the video shows each defect.
The footage is useful evidence. You can show it to your insurer, your landlord or a neighbour who shares the drain. Ask for the video, the images and a short written note of the findings, since a note is easier to share.
Ownership matters too, because it decides who fixes the fault. Your private drain runs to your property boundary. Past that point, or where it joins drains from another property's separate curtilage, it is a public sewer.
Tell the engineer which fixtures have the problem and when. Say what you have already tried, since this decides where to look first.
The camera follows the drain from the affected area outwards. It records each pipe section, joint and connection until it finds the fault, so nothing is guessed.
The cause may be roots, a collapsed section, a displaced joint or a design fault. Ask the engineer to show you the footage, because seeing it makes the options clearer.
Ask for the video, images and a short written note. The note should say where the fault is, because the options depend on that.
Prices vary because drainage systems differ, and so does the time needed to find the fault. A fault that sits near an access point takes less time than one deep in the run.
Ask for a written quote before work starts, because a search can take longer than planned. Ask whether there is a call-out charge, and ask whether repair quotes are separate from the investigation price.
A survey gives a general picture of the whole drainage system, while an investigation starts from your symptoms and follows them to one fault. It may cover the whole system or just the part that matters, because the aim is the cause.
Sometimes. A camera on a rod can pass under a structure from a nearby manhole or chamber. If there is no access point close by, ask the engineer what the options are, since reach is limited.
Footage and a written note are useful evidence. However, your insurer decides what it accepts. Ask your insurer what evidence it needs before you book.