A method of draining a device for extracorporeal blood treatment, wherein the device comprises a dialyzer which is divided by means of a membrane into a first chamber and a second chamber, an arterial line connected to a blood inlet of the first chamber, a venous line connected to a blood outlet of the first chamber, a dialysis fluid line for fresh dialysis fluid connected to a dialysis fluid inlet of the second chamber and a dialysis fluid line for used dialysis fluid connected to a dialysis fluid outlet of the second chamber, a blood pump disposed in the arterial line, a venous expansion chamber disposed in the venous line and an air detector unit downstream of the venous expansion chamber, and wherein the method comprises the following steps of: connecting a patient-side port of the arterial line to a patient-side port of the venous line； generating a negative pressure in the second chamber； operating the blood pump in a first direction and draining the arterial and venous lines in the first direction via the membrane and the second chamber； and stopping the blood pump and draining the arterial and venous lines in a second direction opposed to the first direction via the membrane and the second chamber.
