A cleaning device for cleaning a medical instrument. First and second body portions in a closed position define a flushing chamber. The medical instrument extends through the flushing chamber. First and second sealing members secured to the first and second body portions engage one another to seal the flushing chamber and engage the medical instrument to form a seal thereabout. Portions of at least the first sealing member are disposed within the flushing chamber. Positive pressure in the flushing chamber urges the first sealing member toward the second and toward the medical instrument to enhance the tightness of the flushing chamber seal.