I have a working knowledge of retail fuel dispensers(like 25 years worth). The amount left in the hose and internal plumbing of the unit should not effect the ethanol content of the fuel you are dispensing into your vehicle/boat/snowmobile/motorcycle. The only time it might have an effect is if you are dispensing a very small amount into like an auger or something that has a very small gas tank. And Dave you are correct, no dispensed fuel is 100% what is advertised on the dispenser. There are just to many variables, pipelines, delivery vehicles etc. The fuel has to meet certain parameters but is never 100%. The fuel you get at any retail fueling outfit even has trace amounts of water in it (gasp). The Dept. of Commerce also lab tests the fuel at most sites for octane rating and ethanol content fairly regularly.