A container for storing free-flowing materials including an outer shell having serially connected rectangular shell panels with top flaps forming a top and bottom flaps forming a bottom. The outer shell has a rectangular cross section and includes a cut-out in a lower corner. The container also has an outer liner having an irregular octagonal cross section fitting substantially snugly within the outer shell, with an opening in the lower edge of the outer liner facing the cut-out. An inner liner has the same configuration as the outer liner and fits snugly within the outer liner. The inner liner includes top flaps at the top, bottom flaps at the bottom, and an opening adjacent the outer liner slot. Several reinforcing bands encircle the inner liner. A flexible bladder is located in the inner liner and has an inlet valve near the top and a discharge valve extending through the inner liner opening and retained by the outer liner opening. The outer shell cut-out is removable to expose the discharge valve. A base supports and elevates the flexible bladder. Top and bottom rectangular supports are located above and below the flexible bladder.