A method for keeping constant a pH of a medical liquid being drained from a container includes adding CO2 and at least one other gas or gas mixture to the container during the draining of the medical liquid. An apparatus associated with the method has an outflow for the medical liquid, at least one inflow for the CO2 and an inflow for the other gas or gas mixture, and an electronic control for the determination and automatic supply of a quantity of the CO2 during the draining of the medical liquid.
