Why don't I ever see police cars, ambulances, or fire trucks gas up at the pump?

I'm not quite sure, but if I were to answer, I'd say that it's because they want to do it when they have the least chance of being interrupted by an emergency, so they do it at night, which more than likely has less emergencies than day-time.

Pacific-Pride. At least in Eastern PA. It's like a contract thing. The individual officers don't even know how much the fuel costs, it just shows a gallon amount on the pump. I get a card from my company like a credit card for fuel at any pacific pride.

Corporate pumps. And that's true for a lot of company fleets.

The only one of the type of vehicles I have ever seen at the pump is the police automobiles. If memory serves me correctly, then I have only ever seen them fill up at night, like very late night.

A lot of cities and counties have their own pumps for all departments (ie. water department, parks & rec, electrical, police, fire, etc). It is usually cost effective to buy in bulk.