A vessel has an inner flap and an outer flap that fold across a base of the vessel to form a cover. The inner flap includes a dam tab along the outer edge of the inner flap. When the inner flap is folded down, the free edge of this tab contacts the wall of the vessel and bends upward forming a “folded edge” dam. This folded edge dam can either be one segment or be made of two or more segments divided by one or more V-shaped cuts to allow each segment to fold down and fit together seamlessly. A restrictive channel is formed by the outer and inner flaps together with the “folded edge” dam, which is present in-between the outer and inner flaps.