Pull the manual had to be consulted to find out which flows the detergent only in the low-pressure position of the "Vario-power beam pipe". Ie If one wants the "surface cleaner T250" used with detergent, it is necessary to previously apply the cleaner to the other tube.
The K4 has an additional hose reel, which can be easily refilled detergent compared to K3 and the drive motor is water-cooled. (Most buy the K3, because it costs less to about 80.)
