Mich. Comp. Laws § 125.570: Tanks; construction, testing; underwriter's label.

Sec. 20.

All such tanks shall be welded, brazed or riveted and shall be heavily coated outside with asphaltum or other rust-resisting material. All tanks shall be tested for leakage and shall be tight at 5 pounds air pressure. All tanks having a capacity in excess of 275 gallons shall bear the underwriter's label.