Trenchless methods
Hydro Jetting
High-pressure water strips roots, grease and scale so the pipe can be inspected and lined.
What a jetter does that a cable cannot
A hydro jetter pushes water through a nozzle at several thousand PSI. Rear-facing jets pull the hose down the line and scour everything off the pipe wall: roots, grease, sludge, mineral scale, and the rust flakes inside old cast iron. A cable machine drills a hole through the blockage and leaves the rest on the wall, which is why cabled lines re-clog on a schedule.
Where it fits in a repair
Jetting is step one before lining, because a liner has to bond to clean pipe, and step one before an honest camera inspection, because a line full of roots or scale hides its own condition. It is also legitimate maintenance on its own for a structurally sound line that roots keep finding.
When a line should not be jetted
Cast iron that is paper-thin at the bottom can be opened up by an aggressive descaling pass. A collapsed clay section will not let the hose through. Orangeburg can delaminate under pressure. An experienced operator checks the line first, matches the nozzle to the material, and stops if the pipe is not holding up.
Maintenance versus repair
If the camera shows sound pipe, annual or semiannual jetting is a cheap way to stay ahead of roots. If it shows open joints, channeled cast iron or offsets, jetting is a stopgap and the money is better spent on lining, which removes the joints the roots are using.