So I was at Harbor Freight today and picked up this brake bleeding kit for $30.
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On further inspection it seems to be a gizmo that produces vacuum using shop air. However, the bottle on the left and the clips shown seem to be a clever gizmo for keeping the master cylinder reservoir filled while vacuum-bleeding the brakes. I'm tempted to keep the kit just for this gizmo, unless someone knows an equally clever gizmo for keeping the reservoir full while vacuum bleeding.