A mixing device (100) for generating reaction plastic, the mixing device (100) comprising: a) a mixing chamber (110) for mixing reactive components to generate the reaction plastic; b) a discharge unit (120) connected to the mixing chamber (110) for discharging the reaction plastic generated in the mixing chamber (110); c) a cleaning piston (130) that is axially aligned with a discharge pipe of the discharge unit (120) and is moveable into the discharge pipe to clean the discharge pipe from reaction plastic; d) a fluid supply device for providing a lubricant into the discharge unit (120) via an outlet (142) in order to lubricate the discharge unit (120), wherein i) the fluid supply device is configured to lubricate the movement of the cleaning piston (130) in the discharge pipe, wherein ii) the fluid supply device comprises a gas supply device (140) for providing gas together with the lubricant via the outlet (142) into the discharge unit (120), e) a control piston (115) arranged within the mixing chamber (110) for controlling flows of the reactive components; wherein i) an axial direction of the control piston (115) is oblique, preferably perpendicular, to an axial direction of a discharge pipe of the discharge unit (120). It is also described a method for generating reaction plastic.