Just FYI, E doesn't really mean empty.
Manufacturers purposely do this so that drivers only think their cars are empty so they get gas immediately.
In actuality, there's a few gallons extra below E to allow you time to get gas.
I discovered this from tracking my gas mileage at the pump. I'd be on empty and go for a fill up and the amount of gas that went in wasn't even close to the size of the gas tank.
I figured about 1/5 of the tank's capacity is below E. Oh, that wasn't on a Focus though, lol!