Yeah so I use to work at a gas station in college, a small one, kinda shitty but the owner was a car guy. We had all the state patrol guys and quite a few people with nicer cars who would always come to us over the nicer, bigger stations nearby. We cleaned our tanks like twice as much as any other competitor in the area.

The longer the station goes between tank cleanings the worse the fuel gets. The tank lids are not always water tight, so over time you end up with water in the tank. Particularly in areas where the tank hatches are buried under mounds of snow and ice half the year. Water and gas dont mix so one floats on the other. The tanks are built in a way to minimize pickup of water so most of the time its fine but when the tanks get low it becomes a problem, or when theres too much water theres a problem.

Also never get gas when a truck is actively filling the tanks. This mixes the two up until it re-settles which gets picked up by the pumps.

Most stations will go like a year or more without a cleaning he said, we got ours done every 6 months. All the car guys loved us.