A method for filling and venting a device for extracorporeal blood treatment is disclosed, such as a patient module in a heart-lung machine, without attached patient. A filling liquid from a filling liquid container located higher than the device flows by gravity via a venous side of the system into a reservoir and flows onwards into a blood pump located at the lower end of the reservoir, wherein a first controllable valve (HC1) for a venting line of a filter is opened and, after the response of an upper filling level sensor in the reservoir, is closed. An upper level of the filter is positioned higher than the upper filling level sensor, and a start-stop motion of the blood pump is performed, as a result of which a stepped flooding of the filter is made providing for an advantageous de-airing of the device.