A Drainage Engineer will typically specialise in clearing blockages from drains and repairing or replacing collapsed drains. They are often well equipped and will own costly specialist equipment.
Whilst many plumbers will deal with blocked sinks or toilets internally, quite often, the cause of the blockage is traced to an external drain. Usually, this will then require the engineer to carry expensive, specialist equipment, e.g., High-Pressure Jetting Machines, CCTV cameras or even drain lining repair kits.
For this reason, many plumbers leave this type of work to specialist companies that can investigate and undertake comprehensive investigations, solutions and repairs where necessary.