The pump (1) has a housing (2), a cup-shaped displacement chamber (3), and a connecting duct comprising an inlet opening at the top, and an outlet opening at the bottom. An insertion slot (53) extends from an outer side to an inner side of a lever arm, where the slot extends from a free end of the lever arm. A coupling rod of the insertion slot extends and supports a head (43) of a coupling element above the insertion slot on the outside of a cover (50) of the lever arm. The cover is arranged on an upper edge of a cup-shaped membrane element.
