my gas station for many years has switched there pumps to a one hose set up. there used to be a separate hose for each grade of gasoline pumped. my question is if i buy one gallon of premium for my lawn mower do i get what was left in the hose from the previous customer? so for my one gallon purchase of premium my first one half gallon could be less expensive 87 octane ethanol [censored]. am i correct?