You might not want to wait until it's completely empty. I promised myself I was going to fill up at the halfway point after Rita, but I've slacked off. The good thing is the fact that my tank wasn't all the way full saved me from getting into the stream of refugees trying to leave Houston. I had filled up the weekend before in anticipation of having to make a move, but was off the full mark by evac time and decided to save the gas in case I couldn't get any later, which was the case.
Point well taken. I should try to keep it above 1/2. I do a lot of driving.