Extracorporeal treatment device with automatic emptying of waste bag

The invention relates to a blood treatment device by extracorporeal circulation comprising a filter having a primary chamber and a secondary chamber separated by a semi-permeable membrane; a blood circuit comprising an arterial line intended to come from the patient, the filter's primary chamber and the venous line intended to return to the patient; a dialysate circuit comprising the filter's secondary chamber and at least a drain line for circulating the waste intended to come from the filter and intended to go to a drain; a first bag in fluid communication with the drain line; at least a first gravimetric weighing means linked to the first bag, fluid flow rate adjustment means acting on the drain line; a control unit linked to the first gravimetric weighing means and with the fluid flow rate adjustment means; a second bag in fluid communication with the drain line, the control unit being capable of receiving weight signals from the first gravimetric weighing means and of controlling the fluid flow rate adjustment means to load one of the bags with liquid while the other bag unloads liquid, and vice-versa. The invention also relates to a single-use drain line for use in a treatment device according to the invention.