A closure member for a top opening of a storage bin wherein the storage bin includes a roof with a top opening through which the bin can be filled by material discharged downwardly through the opening; the closure member comprising: a sleeve for engagement with the bin at the opening, the sleeve having a peripheral wall surrounding an axis of the sleeve; the sleeve being arranged to be mounted on the bin at the opening so as to hold the axis to stand substantially upright from the opening with the sleeve extending upwardly from the opening; the sleeve defining an open top end for pouring material through the sleeve into the bin; a cover plate for movement between a closed position covering the open top end and an open position in which the open top end is exposed; the sleeve having a plurality of openings therethrough at angularly spaced positions therearound for allowing vent air to pass between the interior and the exterior of the bin.
