Not sure about the Classic Poire, but on the NG the scavenge (jet) pump moves fuel from the CTR to the No.1 tank, and operates relative to the Fuel QTY in the No.1 and CTR tanks.
The OP test for the system requires 50kg of fuel to transfer in 30mins of pump operation, most tests I've ever done have achieved the 50kg in around 15mins.
Hope this helps.