Exemplary embodiments of pumps, refill units and dispensers are disclosed herein. Some embodiments include a container for holding a fluid and a pump housing secured to the container. The pump housing includes an annular collar for securing the pump housing to the container. The pump housing includes an air chamber and a vent valve located at least partially within the air chamber. One or more air passageways are provided in the collar for providing air to the air chamber. A compressible liquid pump chamber is also located in the housing. The exemplary embodiment includes a liquid inlet valve for allowing liquid to flow from the container into the compressible pump chamber; and a liquid outlet valve located downstream of the pump chamber.