Fuel only starts filling the tail trim tank after 36500 kg is already in the wings. Av fuel burn at higher gross weights 6000 kg/hr. So unlikely you'll see any fuel in the trim for domestic sectors.
Center tank is never used in our long haul ops. The only time I've ever had fuel in the center was when picking up a new aircraft for delivery from Toulouse. Airbus throw in the fuel for free so we filled it to the gunnels (actually max landing weight on arrival here). After the seven hour flight we still had almost enough to reach Sydney - another 13 hours away!
