In the last few months I noticed that my 5 gallon fuel containers were mysteriously taking 5.6 gallons to fill. This was at WaWa.
I called the Dept of Agriculture to ask if that was either odd or normal (barometric pressure related/ temperature related etc).
They told me it didn't sound right and that it only took ONE call in to initiate an investigation.
After looking, the agent told me no one else had called. WTH?
The NEXT DAY when I rode through Wawa I actually saw a Dept of Agriculture vehicle in the lot.
A few days later, magically, I filled my 5 gallon gas container and lo and behold, it took EXACTLY 5 Gallons to the full mark.
I wonder if pumping 5 gallons but charging for 5.6 gallons over several hundred thousand gallons would change the "margins"

Ever filled your tank and that 20 gallon tank held more than that? Should be rare. I have no clue how a gas station owner could change that? Maybe it was just a mechanical error in the stations favor?