A filling apparatus for filling a microplate. The microplate having a plurality of wells each sized to receive an assay. The filling apparatus can comprise an assay input layer having a first surface and an opposing second surface. The assay input layer can comprise an assay input port extending from the first surface to the second surface, a venting manifold formed in the second surface, and a vent hole in fluid communication with the venting manifold and atmosphere. An output layer can comprise a plurality of staging capillaries each having an inlet and an outlet. A venting layer can be disposed between the assay input layer and the output layer. The venting layer can comprise a plurality of microfluidic channels, a flow aperture being in fluid communication with the assay input port and the plurality of microfluidic channels, and a plurality of vent apertures each in fluid communication with at least one of the plurality of staging capillaries. Two or more of the plurality of vent apertures can be in fluid communication with the venting manifold.