Those DOT propane cylinders are product of metal. The metal tanks are powder covered to withstand corrosion. They come with the brand new Overfill Coverage Software (OPD) that is helping stay tanks from being overfilled. As of April 1, 2002 best tanks with an OPD valve may also be refilled. If in case you have a tank with a non OPD valve, you will have to change it ahead of it may be legally refilled. Despite the fact that you’ve got LP for your present tank, you will have to believe shopping for an OPD cylinder with the intention to have it stuffed while wanted.