The fill pipe for such tank or tanks shall be galvanized iron or steel not less than 1 1/2 inches in diameter, extending to the outside of any building, and shall be properly capped at all times. All storage tanks for fuel oil shall be provided with a vent pipe not less than 3/4 inch in diameter with a return bend on the open or exposed end, and the outside opening of such vent pipe, or manhole in outside tanks, shall be covered by a non-corrodible wire screen of 30 by 30 mesh: Provided, however, That vent pipe of such storage tank inside of any building shall terminate on the outside of the building, not less than 10 feet above the source of supply, and that vent pipes from underground storage tanks outside of any building shall not be less than 1 1/4 inches inside diameter and shall terminate not less than 2 feet above grade line. The vent pipe from 2 or more tanks may be connected to 1 upright provided they be connected at a point at least 12 inches above the source of supply.