Available at any auto parts store and on Amazon. Costs pretty much the same everywhere. The Crossfire's fuel capacity is about 16 gallons so for routine storage and cleaning you add the entire 16 oz can to the tank but you could even double that to 2 cans for more serious cleaning of the system. It's not going to harm anything. It's been around forever and got its start in the harsh marine industry and environment. Hence the name "Sea Foam".