Check your tank for cracks and corrosion as these could be signs of an impending leak
Make sure your tank is kept on a solid, level surface, far away from buildings and water courses. If any oil gets into the water system, it could cost in excess of £30,000 to clean up. Ouch!
If your dark green plastic tank now looks pale, it could have been bleached by the sun. This makes the plastic brittle and prone to breakage. If your tank is metal, keep an eye out for coppery rust too.