A medical drainage device is provided which includes a casing and a chamber for indicating the amount of suction applied to an animal or human body by the height of a water column. A fill funnel is further provided, which is attached to an opening in the casing for filling water through the opening into the chamber. The fill funnel has a configuration rendering the fill funnel selectively impermeable. A fill funnel and a method of manufacturing a fill funnel are also provided.
