A device for expressing milk from one or more breasts has at least one, and preferably two expressors and a pump. The expressors each have a cup for fitting on the breasts and a cup outlet to which a vacuum created by the pump can be connected. A filter that is substantially permeable to air but substantially impermeable to milk and water prevents milk from entering the vacuum pump. The filter is preferably permeable to air even when wet, though, so that the device can still be operated, even as the filter collects fluid.