Not much. They suck most of the left of fuel back into the tank when your done fueling. The remaining fuel in the hose will drip out once you've selected what you want and the pump turns on.

 

I Had seen something on the news about the Weights and Measures. When they go to test the fuel from the pumps for quality and price, they said they run 2 and a half gallons out of the hose before they start testing it, because the grade of fuel used before it can still be mixed in within the first 2 and a half gallons.

 

That's what I was thinking. They aren't as common but if you find one near home, you can fill up there most of the time.