I think we need to remember that the straight gas fumes in a fuel tank are "above the upper flamable limit", and will not ignite, until you allow air containing oxygen to enter the tank. At that point, you have completed two sides of the fire/explosive triangle, where all you need from that point, is a very small static electricity spark, or tool strike, causing a spark, to cause a good explosion of the tank, or in the very least a fire at the tank opening.
If a person came up with a air operated eductor, as suggested earlier in this thread, the idea may work successfull, providing the suction hose is large enough.
Again.....the fumes coming out of the eductor discharge, will be highly combustable. Vent outside and away.
Be Carefull......Please !!