A collapsible container for the storage and transport of flowable material. The container is provided with a continuous sheet of side panels secured into stepped engagement with itself to define an interior. Foldable support brackets are secured to the side panels to maintain the side panels at an angled orientation relative to the side panels of the container and to prevent distortion of the side panels by hydrostatic pressure toward a circular orientation. The support brackets define an opening in the top of the collapsible container through which a fill head may engage a top cap of a flexible liner provided within the collapsible container, to fill the liner with flowable material.