Inundation, part 2:
My wife told me, what happened: they came with a machine that gave a giant pressure (15 times of a racing bike pressure) into the discharge pipe and after a long time of fearful waiting ("if it doesn't work we must open the wall") it made PLLOPPP and the pipe was free.
Explanation: when they had made the new shower and toilet discharge, they removed the upper part of the pipe (that one which leads to the roof) and replaced it by a plastic exhausting pipe. BUT: there were many clinker and rust pieces from the old pipe and mortar from their work which had vanished in the lower part of the pipe.
to be continued???
P.S.: this is dedicated to Frank Zappa and his "Flakes" song (you know what I mean?)