The top flaps on the cereal box should already be open. Then you must open the flaps on the bottom of the cereal box (the side parallel to the opening) and flatten it. Now use the creases made by the corners of the box and fold them inward; it should be flat again. Fold it length wise thus leaving a little rectangle of the flattened box that is not overlapped by the other half of the flattened box. Tax this tab and insert it into the opening in the adjacent half of the cereal box. Your cereal box is now a manageable size and can easily fit in the trash can.