Abstract: A double wall tank for the storage of liquids is manufactured from a rigid, inner tank by helically extruding a synthetic resin outer sheath over the sidewall portion inner tank while preventing bonding between the extruded outer sheath and the inner tank, with outer end portions that are sealingly bonded to the outer sheath sidewall portion.

Abstract: A multiple wall tank for the storage of liquids is manufactured from a rigid, single wall inner tank having at least one aperture by applying an outer sheath over the inner tank, removing a portion of the tank surrounding the aperture, applying a layer of a synthetic resin material to the inner tank exterior surface surrounding the aperture, providing a spacing means to provide for substantially free passage of liquids between a substantial portion of the inner tank and the outer sheath and bonding a portion of the outer sheath to the synthetic resin layer surrounding the aperture to form a substantially liquid impervious seal around the aperture.

Abstract: A multiple wall tank for the storage of liquids is manufactured from a rigid inner tank having at least one aperture by applying a layer of a synthetic resin material to the inner tank exterior surface around the aperture, providing a spacing means to provide for substantially free passage of liquids along at least a portion of the inner tank, applying over the layer of synthetic resin and the inner tank an outer sheath of a thermoplastic synthetic resin material, and bonding the outer sheath to the resin material layer surrounding and proximal to the aperture to form a substantially liquid-impervious seal around the aperture.

Abstract: A multiple wall tank for the storage of liquids is manufactured from a rigid inner tank having at least one aperture by applying a layer of a synthetic resin material to the inner tank exterior surface around the aperture, providing a spacing means to provide for substantially free passage of liquids along at least a portion of the inner tank, applying over the layer of synthetic resin and the inner tank an outer sheath of a thermoplastic synthetic resin material, and bonding the outer sheath to the resin material layer surrounding and proximal to the aperture to form a substantially liquid-impervious seal around the aperture.