This paper describes the design and the construction of the stainless steel tank of the JSNS$^2$ detector. The leakage was examined using water and gas after the construction. The new sealing technique with liquid gasket was developed, and its sealing capability was evaluated quantitatively. The result shows over 5 times better value than the tolerance level of leakage.The acceleration measurement during the transportation of the tank shows adequate robustness.These tests prove that the stainless steel tank is feasible to use the real experiment.