Fuel tank connections

[Steve_D]

Just about to start running in my fuel lines.
Using the standard factory config. pipes go from tank to pump, non-return valve, tee piece, filter, carb.
Other pipes go tank to tank both at the top and bottom.
Question, When you fill tank 1, tank 2 will also start to fill but will it fill very quickley or do you still have to go round the other side and fill tank 2?
Steve