Abstract: An inlet/outlet, rotomolded, flexible containment fitting for polyolefin double wall vessels attachable externally to a vessel's outer, sidewall. The molded flexible containment fitting having a corrugated wall portion and circular flanges at each end, one of which is attached to the outside of the containment vessel with the opposite flange having a pipe member extending internally through the fitting a pipe flange attached externally to the inner vessel wall thereby providing compensation for deflection, alignment, expansion and contraction of the inner vessel relative to the external containment vessel while still maintaining a secure fluid conduit through both the inner and outer vessel walls.

Abstract: A containment tank assembly for the safe storage of liquids wherein an enclosed storage tank is positioned within an open-top containment tank. A space is provided between the adjacent side walls of the storage and containment tanks for receiving any leakage from the storage tank, and a roof extends over the space between the side walls to prevent the leaked liquid in the space from becoming contaminated with rain water.

Abstract: A plastic tank fitting having a circular flange portion molded integrally with the exterior surface of the plastic tank side wall adjacent to the tank bottom wall, and concentric with a drain opening in the tank side wall. Approximately 240.degree. of the upper portion of the flange is flush with the tank side wall, while approximately 120.degree. of the lower portion of the flange extends downwardly from the tank side wall adjacent the tank bottom wall. A flange and associated pipe fitting are bolted to the molded circular flange portion.