The present invention relates to extracorporeal blood treatment devices and methods and devices for conserving extracorporeal blood treatment devices. In accordance with the present invention, an antifreeze agent in introduced only into that part of the dialysis liquid system of the blood treatment device that includes the volume lying upstream of a sterile filter with which sterile substituate is recovered from the dialysis liquid. Accordingly, that part of the dialysis liquid system that includes the volume lying downstream of the sterile filter is not filled with an antifreeze agent. The present invention makes it possible, after removal of the sterile filter, to easily and safely separate a substituate segment from the rest of the dialysis liquid system and drain off liquid located in the substituate segment.
