A gas station that gets a fill every two weeks on an 8000 gallon tank, sapping the tank top to bottom, will average 6 ten gallon fills per hour. He's basically saying to stay away from any gas station that's completely nowhere near anything, mostly because it's probably closed because sales were so dismal.
I'm interested in hearing how you can draw gas from an underground tank from the middle - not the top, not the bottom - just because they fill three times a week. The tanks I'm familiar with (found in truly populated areas!) feed their pumps at the bottom and filter the fuel before it gets to your nozzle. It's a matter of physics supporting getting the fuel above the pavement.
How much sediment could you get in an underground tank? Think about it - it's getting diluted by thousands upon thousands of gallons of gas a week.
You'd pretty much have to be at the gas station at the end of Terminator to be concerned about trouble from the tank.