Subtract a tube from a wall

[cpot]

Hello,

Sorry to ask so many questions, but the trial will not last long.

I want to cut a hole in the wall or at least make segments from the intersect of the tube and the wall.

I understood that the tube and the wall must be an 'Object', selecting all surface was not enough to do boolean operations. I created then 2 objects.

Then as one is not a closed object (wall), i have been advised to use "knife" which i did.

Then i go the second screenshot, not exactly what i expected :-)

Best,
Chris