I try the same things but its not easy getting it in time. It comes up fast and it pours about a cup out the neck before it shuts off. Then, today, I carefully put about another gallon or two in it to get it to the top, just to see how much it takes. All the manuals say 18 gallons, but others on here say less. I'm sure with all the sender and pickup issues many people seem to have, it has a couple unuseable gallons in it.