well, how big of a tank is it? (1lb or like a 15lb, what engine is this going on, what frame is this going on etc)
you could try to fit it on the back if you have a rear rack. and pumb it from there. that or put it on like a gas tank on the front.
you could also put it on the down tube, or put it like a water bottle (if you frame has enough clearence)