Fixed or rotating nozzles with partially rearward facing jets create thrust which pulls the hose into the pipe. The spent water then flushes the debris to the open ended pipe. As pipe diameter increases, more flow is required to provide adequate flushing & nozzle centralisers are used with extension arms to keep the nozzle close to the pipe wall for maximum impact.
The Rotocar Cleaning system allows very long pipe runs with multiple bends to be cleaned from one end. A special unbalanced nozzle hugs the pipe wall while the hose is rotated & fed into the pipe.