Do Plastic Gas Tanks Need to Be Cleaned?
Prior to the existence of plastic gas tanks, the metal ones had a specialized plastic lining that would degrade over several years and fill the inside of the tank with debris. It was thought that making a solid plastic tank would fix this, and while plastic debris is not a problem, other problems have still arisen. When gasoline is left sitting in a tank for a period of months or even years, it separates, leaving a solid sludge at the bottom.
Sometimes this sludge breaks up and is carried off into the engine by the fuel lines, which will clog the air filters very quickly. What’s even worse, rust and bits of burned carbon can flow back from the engine into the tank. For that reason one should clean out gas tanks every few years–more frequently if the tanks contained mixed gas or are rarely used.