Method of making a multiple wall storage tank having an extruded outer jacket bonded around an aperture

A method of manufacturing a multiple wall tank for the storage of liquids comprising the steps of:

• providing a rigid, inner tank having generally cylindrical sidewall portions of a predetermined length, end portions generally transverse to said sidewall portions and a central axis extending generally longitudinally between said end portions, said inner tank having an exterior surface, and at least one aperture formed through said inner tank;
• helically extruding an outer sheath formed of a plurality of partially overlapping layers of a substantially liquid-impervious synthetic resin material over said inner tank, with each successive overlapping layer having a predetermined width substantially less than the axial length of said inner tank sidewall portions, an inner surface and a leading edge;
• providing a spacing element intermediate at least a portion of said inner tank exterior surface and said outer sheath to provide for substantially free passage of liquids between a substantial portion of said exterior surface of said inner tank and at least a portion of said outer sheath;
• removing a portion of said outer sheath surrounding and proximal to said aperture to define a portion of said outer sheath having a periphery around said inner tank aperture;
• subsequent to said removing step, applying a thermoplastic synthetic resin material to a portion of said exterior surface of said inner tank surrounding and proximal to at least a portion of said aperture to define a layer of said thermoplastic synthetic resin material surrounding and proximal said aperture;
• providing an adhesive interface between said resin material layer and said inner tank exterior surface to promote adhesion thereof between said inner tank exterior surface and said resin material layer;
• and
• bonding said outer sheath to a portion of said resin material surrounding and proximal to said aperture such that a substantially liquid impervious seal is formed around said aperture.