I don't know about that test but the drain for the CCV goes below the oil level so that it acts like a vacuum break for the cyclone, so yes, there should be bubbling if you force air down it.

I don't remember how hard it is to get to the vacuum hoses from the vacuum manifold to the CCV but if you can block/disconnect those (it might be a tee 2 into one) it might help to eliminate some things.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)