Back at the family farm when I was a kid, circa early 1970's, we had our own hand pump 200 gallon gas tank. One of my tasks was to fill up Dad's '72 C20 when he got home from work.
I got pretty good at listening to the escaping gas fumes as I pumped in the gas. As soon as the tone changed I would stop.
This would leave a couple inches empty at the top of the tank, which was enough to prevent overflow due to expansion.
