Disclosed herein are exemplary embodiments of linings, liners, and methods of providing a liner or lining for a tank. An exemplary embodiment includes a method of providing a liner or lining for a tank. In this exemplar embodiment, the method includes extrusion welding a pair of sheets together by infusing a molten thermoplastic material along an interface and within a gap between the pair of sheets. The method also includes extrusion welding the pair of sheets to a bottom sheet by infusing the molten thermoplastic material along and between the pair of sheets and the bottom sheet.