Abstract: So that a freight or storage tank for bulk material, that has at least one long emptying hole on the bottom, can be closed and opened, the tank has at least one flexible belt that extends essentially over the length of the opening and whose one end is attached to the tank, and under which is a roller or roller system that is approximately of the same length and that supports the belt when in the closed position and that can be removed from the closed position, as well as elements to move the roller or roller system across the opening between two extreme positions.