It is surprising how good a 20 year oil tank can look. As you can see from the inside the sides and upper parts still look like new shiny metal, but pan down to the bottom where you will see it show its age. This is how a typical oil tank will fail – from the inside out. Water accumulates in the tank and since it is heavier than the oil it settles at the bottom. If this water is allowed to accumulate and stay in the tank it will eventually cause corrosion. Oil tanks should be installed with a slope. This will drain any water buildup through the burner. The importance of this slope is often negated by installers opting for ease of installation. Tanks with the spigot on the side, rather than the bottom of the tank, will trap water more easily as the spigot cannot be mounted as low due to the tanks design. Also of interest, note in the forefront, the float for the fuel level gauge.