Abstract: An improved double wall tank has two or more threaded fittings, with a steel outer tank and a thermoplastic inner tank. The inner tank is formed within the outer tank by rotational molding. The inner tank is bonded to the outer tank in an area of the fittings, but is otherwise separate and apart from the outer tank. Before carrying out the rotational molding process, bonding material is applied to the outer tank in the area of the fittings. The thermoplastic material is in powder form and includes mold release material. The thermoplastic material is inserted into the outer tank before rotational molding. The degree of shrinkage of the inner tank can be controlled by air pressure including an area between the fittings.

Abstract: An improved double wall tank has two or more threaded fittings, with a steel outer tank and a thermoplastic inner tank. The inner tank is formed within the outer tank by rotational molding. The inner tank is bonded to the outer tank in an area of the fittings, but is otherwise separate and apart from the outer tank. Before carrying out the rotational molding process, bonding material is applied to the outer tank in the area of the fittings. The thermoplastic material is in powder form and includes mold release material. The thermoplastic material is inserted into the outer tank before rotational molding. The degree of shrinkage of the inner tank can be controlled by air pressure including an area between the fittings.

Abstract: A temporary closure for containers such as storage tanks and the like has a cap portion with arcuate thread supports extending downward from a lower surface of the cap portion. The outer surface of the thread supports has screw threads thereon, the screw threads corresponding to screw threads on an inner surface of a tank opening. The closure is made of a one piece plastic material and the thread supports are flexible enough so that the closure can be quickly and easily inserted longitudinally into the tank opening with the screw threads on the closure overriding the screw threads in the tank opening. The closure is held in place in the tank opening by the screw threads and can be removed by turning or by prying the closure out of the opening with a suitable tool.