A precast, prestressed concrete tank and method that facilitates construction of a primary inner tank within a secondary outer tank, and which permits for the construction of the primary inner tank after the secondary outer tank has been erected, but without requiring insertion through a top of the secondary outer tank, or by tunneling underneath the secondary outer tank, is disclosed. The primary inner tank has an inner wall and the secondary outer tank has an outer wall (precast, prestressed concrete) and wire windings. The primary inner tank is disposed inside of the secondary outer tank. The secondary outer tank has a plurality of first precast outer wall panels, and a temporary construction opening frame. The temporary construction opening frame defines an access doorway during construction of the tank. The temporary construction opening frame is disposed on a foundation base slab.