A storm water drain tank module for assembly into a storm tank for storage of storm water includes a top platen, a bottom platen and a support spacer. The top platen has an upper surface and a top platen peripheral edge. The bottom platen has a bottom surface and a bottom platen peripheral edge. The support spacer is attached to the top and bottom platens to space the top platen relative to the bottom platen. A plurality of tabs and a plurality of slots are defined proximate the top and bottom platen peripheral edges, respectively. Each of the plurality of tabs extends outwardly away from the top and bottom platen peripheral edges, respectively, and each of the plurality of slots extends into the top and bottom platen peripheral edge. The plurality of slots is open in a lateral direction.