Easiest way
Lots of chandlaries sell oil in pre-measured containers for mixing with gas for outboards. I don't know exactly what grade of oil is used, but they come in a 16 oz. size for mixing in a standard 6 gallon fuel tank, and in an 8 oz. size for mixing in a standard (you guessed it) 3 gallon tank. Since a U.S gallon equals 128 U.S. fluid oz., this works out to a 48:1 gas to oil ratio. Close enough to the 50:1 as to make no difference. Most standard bottles of motor oil also come with a measuring "window", so that you can accurately gauge how much oil you use when pouring from the container. Most manufacturers recommend that you put the oil into the gas container first, then add the gas. This should adequately mix the stuff togther.
