Either buy an electric fuel pump to empty the tank and burn the old gas in an open container.
Gas doesn't burn, only gas fumes do, so if the container is open it will be actually hard to light. Once the gas beneath the flames starts to heat up, more gas will evaporate, and the flames will grow taller; so protect things like trees and buildings around where you are burning it.
Otherwise have the car towed to the garage and have the mechanic there take care of the problem. You want the tank dropped and cleaned out, the gas lines blown out with compressed air, and gas filter changed, The carb can be cleaned out, but it will run better and be more reliable if it is rebuilt, as the gaskets shrink when dried out.