Abstract: The invention relates to an apparatus for sucking liquid, in particular blood, from a collecting location, through a suction conduit (4) having an inlet end (5), wherein a liquid additive, in particular a CPD solution, is fed through an outlet end (15) of a conduit for additives (13). The inlet end (5) and the outlet end (15) being fixated in respect of and close to each other such that the additive is fed out to the collection location (16) close to the inlet end (5) and is mixed with the liquid that is being sucked before it enters the inlet end. A dosage unit (12) is controlled in dependence of the sub pressure in the suction conduit (4) for to regulate the feeding of the additive in dependence of the quantity of liquid being sucked.