Searching for the answer to my question above, I made some tests.I tried to rotate the capping station with an electric screw driver. Slowly, miming the same speed and pattern from the ink charging. It sucks a bit in the beginning and then it stops. I didn't ruin anything but when I tried a nozzle check after, all the nozzles where empty. Probably it creates some vacuum and then it sucks the ink back from the head. After a couple head cleanings it started to print again.
I disassemble the ink system from a R3000 and play a bit with it. I noticed that the ink, in order to flow, it had to be pushed not only sucked by the capping station. If it's not pushed some valves are blocking it. So in order to make an ink purge not only the capping station has to be controlled but probably the air pump too. Any thoughts? It gets already to complicated... Should we ask Andy to close the topic