siphon it out and throw lit match in. That way you'll just burn of all the fumes.
I take no responsibility for your actions that result from reading this thread.
Seriously though, just leave the cap open for a few days with a blowing across it. Gasoline evaporates VERY quickly and as the gases rise the fan will push it away, and dense air will drop in to replace it.
Or you can just remove the tank, drop the fuel pump, wash it, (change your fuel filter while your at it casue youll never want to do that again) then let it air out. I did that to my tank and it was gas fume free in minutes.