was loosing coolant due to a split hose
make sure the heater matrix is flushed through also
never heard of the rad pipe being sucked in - it is usually the opposite where it bulges and expands under pressure thus cracks appear as it ages and wears
when flushing coolant i usually leave the cap half tightened and take the car for a spin - knowing i might loose coolant at least any air will eventually release from the expansion tank
on the astra 2.2 i can see coolant passing through the expansion tank at idle when reached temps but on the vectra 2.2 i hardly saw any passing coolant at idle at temps - whether it is the size of the engine bay and higher temps i dont know
