this invention relates to a container consisting of a thermoplastic material , with side walls , flat top and bottom panels of which the top panel is provided with at least one fill / drain opening , and with a continuous circumferential carrying and transport rim . for better utilization of pallet space , the container body has an approximately square cross - section with slightly convex lateral surfaces and slightly radiused corners . in order to counteract the inherent tendency of the flat container walls to bulge and buckle , the container body is provided with vertical and / or horizontal reinforcement elements .