a stationary container with straight , vertical walls and an open top has a bottom frame with an array of holes through which closely packed support cells can slide so that the base of the container roughly contours to the surface on which it is set while maintaining a level top surface . this arrangement allows the load of a contained fluid material to be applied normal to the top of each support cell , distributing the vertical load over multiple points between the bottom of the container and the load - bearing surface on which the container is set . the support cells may be solid , hollow , or have openings to allow fluid to pass between the interior and exterior of the container . the container walls are vertical and attach to adjustable corner posts . the container may have a second frame , with or without holes , positioned above the support cells in order to provide additional support for the container walls , distributed support for additional loads applied to the top of the filled container , downward stabilizing support for the load , or a conduit for a second fluid .