They fill on pressure differential.
We had a liquid hose which was attached and turned on. Then the bleed/80%level valve was opened. This dropped the pressure of the tank being filled a little below the supply tank. Depending on conditions the tank fills at a modest rate.
Now, you come in at say noon with everything all warmed up and need fuel. The tractor tank will be at a significantly higher pressure. We would grab a bolt and bleed pressure off fast on the vapor valve. Crude but it works and under these conditions you had to bleed it a lot or it would take forever.
If you can catch the tank almost out and/or at low pressure it will fill fast.
There are pumps but I never had one. When the liquid starts coming out the bleed valve (generally) shut it off.
We had a 500 gallon tank on a trailer to take to the field if wanted. You do burn more.
RT (and my 2 cents.)