The screw-on spouts for metal and plastic gas cans often don't seal tightly, allowing gasoline to leak at the fitting and dribble down the can when fueling mowers and equipment. This not only wastes increasingly expensive gasoline, it also exposes you to the fuel's toxic properties. To stop leakage, use an oversize rubber gasket matching the diameter of the can's spout, and seat the gasket directly on the can so the spout screws down snugly against it. These gaskets are very inexpensive and available from the plumbing section of hardware stores. In addition to discouraging needless spills and evaporation, a tighter seal helps prevent stored fuel from releasing hazardous fumes.