A wall-base joint for a concrete tank is constructed by providing in a base a groove larger than the width of a tank wall, placing the wall in the groove to leave a groove portion on each side of the wall, prestressing the wall with a first compressive force, filling the inner (with respect to the center line of the base) groove portion with concrete and curing it to form a first plug therein, prestressing the wall further with a second compressive force to counteract a fraction of the bending moments produced by the liquid in the tank when it is full, and filling the outer groove portion with concrete and curing it to form a second plug to lock the inner plug into permanent compression.