A plug-in pump includes a cylinder and a pump housing, wherein the cylinder has a cavity in which a movable piston is accommodated, wherein a first end of the piston delimits a pump chamber, and a second end of the piston is connected to a drive device for the piston. An inlet valve is arranged in the cylinder, which inlet valve connects the pump chamber to a feed line for a first fluid, and an outlet valve connects the pump chamber to an outlet. The pump housing has a cavity that forms a first chamber connected to a feed line for the first fluid, and at least one second chamber which is separated from the first chamber and which is connected to a fluid system of a second fluid. The first chamber is fluidically sealed off with respect to the second chamber.