Abstract: The invention relates to method of filling a medical washer/disinfector. A desired pump speed of a circulation pump is determined. A predefined filling level associated with the desired pump speed is identified. Liquid is fed into a washing chamber while the circulation pump is running at less than said desired pump speed. While the liquid is continued to be fed so that the liquid level rises, the pump speed is increased based on the rising liquid level until said desired pump speed is reached. When the pump is running at said desired pump speed, it is detected when the liquid has been filled to the predefined filling level, and upon such detection the feeding of the liquid into the washing chamber is interrupted. Then invention also relates to a method of operating a medical washer/disinfector, a control unit and a medical washer/disinfector.