aristoclis
Actually even with full center tank feeding engines when inners are at 3t, I am not sure if fuel return is able to top up the wings again.
Next time you fly with a reasonable quantity of centre tank fuel monitor the wing tanks to see what happens.
I say again - 3,000 kg has no significance as far as I am aware. It gives you time to monitor the leak for 30 minutes, and then reminds you to switch the centre tank pumps back on for the rest of the flight. It's really very simple.