Abstract: A closure system for a trough comprising a first closure member and a second closure member, the first closure member being movable between a closed position, where it closes against the perimeter of a first opening in the bottom of a trough and an open position where it retracts to a position away from contact with the perimeter of the first opening, the second closure member being movable between a closed position where it closes against the perimeter of a second opening in an opposite side of the bottom of the trough and an open position where it retracts to a position away from contact with the perimeter of the second opening, and first and second controllers operable to move the first closure member and second closure member respectively between the open and closed positions.