Foam dispenser systems and pumps for use in foam dispenser systems are disclosed herein. A refill unit for refilling a foam dispenser system comprises a container for holding a supply of foamable liquid and a pump housing connected to the container. The pump housing comprises one or more connections for connecting to one or more external air pumps, wherein the air pumps supply air pressure to move the foamable liquid into a mixing chamber and to mix air with the liquid in the mixing chamber and create a foamy air-liquid mixture.