Foam dispensers having integral air compressors with connectors to connect with a disposable refill unit, disposable refill units and liquid pumps are disclosed herein. A refill unit includes a container and a liquid pump. The liquid pump includes a liquid chamber defined at least in part by a liquid inlet valve and a liquid outlet valve. A piston that reciprocates horizontally in the liquid chamber. A mixing chamber is located downstream of the liquid chamber. The mixing chamber is in fluid communication with the liquid chamber and has an air inlet. A sanitary seal is located proximate the air inlet to prevent liquid from contaminating the air compressors.