(a) Filling and discharge lines for Class I and Class II liquids, and for Class III liquids where practicable, shall enter tanks only through the top and shall be graded toward the tank.
Fill openings
(b) The fill-pipe opening shall be located outside of any building. For Class I or II flammable liquids storage the fill-pipe opening shall be not less than 5 feet from any door or cellar opening. For Class III flammable liquid storage the fill-pipe opening shall be not less than 2 feet from any building opening at the same or lower level. The fill-pipe opening shall be closed and liquid tight when not in use. Fill-pipe for filling by tank car or tank truck shall be not larger than 4 inches nominal inside diameter and shall be not constricted. Fill-pipe openings shall be identified by a definite color scheme or other means.
Gauge openings
(c) Gauge openings, if independent of fill-pipe, shall be provided with liquid-tight cap or cover. Where Class I or Class II liquids are stored within a building, such gauge opening shall be protected against vapor release or liquid overflow by means of a spring-loaded check valve or other approved device.
Drainage of tanks in buildings
(d) Inside storage tanks for Class III flammable liquids shall be provided with draw-off or drain openings. Tanks shall be installed so that the bottom pitches to the draw-off or drain openings at a slope of not less than ¼ inch per foot of length. The draw-off or drain opening shall be provided with suitable connection to provide a sump from which water or sediment can be drained readily.