In the first stage the rehabilitation section has to be put out of action by implanting barrier bubbles or barrier discs at the cleaning- and inspection openings of the base lines in the basement. Then it has to be cleaned.

The cleaning is performed with a HD flushing method. They start at the last chamber (end chamber) and the high point of the collector DN 300 and end at the chamber in the main collector DN 600, the end of the rehabilitation section. The road gullies and their connecting channels as well as the rainwater lines  are flushed separately from the ground surface.