Abstract: The present invention relates to an apparatus for disinfecting a hydraulic circuit of a device for processing liquids for dialysis, wherein the apparatus comprises: at least one valve arrangement; at least one source for disinfectant; at least one first line which is connected or connectable to the source for disinfectant and to the hydraulic circuit; at least one second line which branches off from the first line and is connected to environmental air or to an air reservoir; wherein the valve arrangement has at least one first valve and at least one second valve which are located in the first line in front of and behind the point of the branching off of the second line from the first line; and wherein the valve arrangement furthermore has at least one third valve which is located in the second line, with the first and second lines being arranged such that, with opened first and third valves, the second line and the first line are ventilated between the second valve and the source so that the disinfectant cont