If you can't run out all of the fuel out then use your fuel bottle to remove it. If you leave fuel in the tank condensation / moisture will build up in the tank, and when you run you vehicle the next time you are running that moisture through your engine. Be careful not to over oil your engine if you use a starting system that requires a oneway bearing, because you can cause the bearing to start slipping. Same thing if you run a fuel with a high castor oil cotent.