How do oil companies fill three grades of gas from a single tanker with one hose?

Anytime I see the tanker at the gas station, a single inground tank seems to be getting filled from a single hose coming out of the one tanker, and suddenly we have three different octane rated gasolines!How do oil companies fill three grades of gas from a single tanker with one hose?
I used to work at a gas station. We had 3 tanks underground and they would not be filled on the same day. each delivery would be a different type of gas. There were 4 different hatches in the parking lot. ( We had deisel also)How do oil companies fill three grades of gas from a single tanker with one hose?
Usually its one long tanker coupled to a short one...I believe the long tanker actually has two tanks separated with a baffle..so now you have a Truck trailer carrying 3 grades of fuel...I guess you could have a long tanker with 3 separate tanks also..
They only fill one grade at a time. Walk up to the truck. It normally has several outlet valves for the different grades, and there are separate tanks underground, with separate fill tubes for each one. usually for regular and super, and maybe diesel. Mid-grade is often mixed at the pump.
If you go look in the area where the tanker downloads, you will notice there are three or four manhole covers, indicating there are three or four underground tanks. The tanker driver only downloads to one underground tank at a time, and may, or may not carry more than one grade of fuel in seperate compartments inside the tanker trailer.
the gas tanker has different compartments for different fuels also they receive an order before they show up so they now how much to put in each tank... now it may appear like they only dump to one whole and that is possible if they were only filling like diesel or a grade that at the station had a much bigger tank. but they dump into different tanks.
Multiple compartments and valves .