Abstract: A sectional panel tank comprises one or more side wads that are joined together in forming the sectional panel tank. One of the side wall comprises a first unit panel having a first extension at a first edge of the first unit panel and a second unit panel having a second extension at a second edge of the second unit panel. By combing the second extension to the second extension, the second unit panel is joined to the first unit panel for providing a continuous surface of the side wall. No gasket is needed between the first extension and the second extension. A method of making the sectional panel tank is also disclosed. A method of making prefabricated unit panels with lining sheets is further disclosed for the sectional panel tank.