I had the low fuel light come on right when it switched to one bar on the fuel gauge. Then drove around 10 miles to the gas station.
I'm not sure if they used any special methods to fill the tank (waiting until the evap system fills up, bouncing the car to get rid of bubbles, tilting the car) but the top two insights with the longest range used 13.4-13.7 gal.
The Insight Marathon 2006 -- World Record 2,254.4 miles on one tank of fuel - CleanMPG Forums
Also, my first 85mpg trip! Pretty hilly freeway, I camped out behind a rig following two seconds behind and used him more as an excuse to accelerate slowly than drafting.