Hello,
So I can say that I just put a piece of hose in a big tank of fresh water and use the pressure washer and it works perfectly.

No, the K Mini does not have a suction mechanism and therefore cannot suck in water from a tank, for example, when operating correctly. Only models from the K4 series upwards have one.

Note also that the water supply must deliver 7 litres per minute, which may not be the case in all private homes.