The invention relates to a suction device (1) for removing a mixed fluid, in particular fecal matter, from a collecting tank (2), in particular from a sewage tank of a railway vehicle, comprising a mixed fluid inlet (4) for receiving the mixed fluid, said mixed fluid inlet (4) being fluidically connectable to a connection port of said collecting tank (2), a mixed fluid outlet (8) for discharging the mixed fluid, said mixed fluid outlet (8) being fluidically connectable to a suction line, and a flow channel (14) extending between said inlet and said outlet.The invention relates in particular to a constriction member (10) which is adapted to reduce a cross-section of the flow channel (14) in sections thereof or along the entire length thereof.The invention further relates to a suction station for removing a mixed fluid, and to such a method.