[goodhart]

I doubt there would be any sparks if you were to drill, even if there were the gas pouring onto it would more than likely just drown it out. Vapor light way easier than liquid gas. When my grandpa used to own his body shop and he would patch a tank, he would weld it with the tank full because with it empty it would have a lot higher chance of igniting where a full tank it would drown it out if he burned through.

Besides, gas tanks are so thin the drill bit would probably only make a few turns until it pops through, it wouldn't have time to get hot let alone create sparks.

I would check for a drain plug just in case before messing with anything else though, shouldn't be too hard to spot.