But yes, you would be best to drain the fuel to avoid sucking bad fuel in. I have forgotten to add fuel stabilizer to a boat and let it sit for 8 months before. Fuel still smelled good, didn't darken in color, and ran fine so I ran the full tank with no issues. Chances are you will be fine, but to be safe it would be best to drain the tank. If you decide to not drain the tank, I would recommend filling the tank. Then on your next tank add some fuel injector cleaner just in case. Otherwise, your battery might be a goner and your tires might have flat spots. Oil change would be best.