Fuel tanks

[Racing Roj]

I have run both tanks down to zero on each tank via the dashboard switch but one tank took 40 litres and the other 10 litres.
The last 10 litres in tank 1 took forever to fill.
Is there a way of calibrating the senders or gauges as it would appear they are showing empty but aren't.
Also when filling does one tank partly fill from the other?

[Racing Roj]

Steve
Thanks for that.
I don't understand though if each tank holds 7 gallons (32litres) why I could only get 50 litres in when the gauges showed empty.