Abstract: A tank trailer has a container formed from a tubular body and one or more polar bosses coupled to distal ends of the tubular body. The trailer includes a pumping system that has one or more pipes fluidly coupled to the interior of the container via an interface at one of the polar bosses. The tank trailer may have a base support and one or more circumferential support members coupling the base support to the composite container, or the support functionality of the base may be instead accomplished by the container. The one or more polar bosses may include an inner circular surface and an outer circular surface, wherein the outer circular surface has one or more flat portions that complement and engage one or more concave features of the substantially tubular body.