The vacuum hose is a mystery to me. Maybe to BMW as well, since they deleted it in later versions.Interestingly, that confused me because Aioros' routing points conflicted with cn90's information (valve cover) and that of realoem.
So, I went with the cn90 & realoem end points when I annotated the diagram and cn90's picture (which we both annotated) as shown below.
RDL: For those E39's that 'do' have the vacuum hose, can you hazard a guess as to WHAT it does and whether the direction of vacuum is IN or OUT?
Normally I'd 'assume' the direction of vacuum is OUT but there are two huge hoses within inches of that vacuum line which are connected directly to manifold vacuum (not to the VANOS) ... so that's why I ask if the vacuum is inward or outward in that small line.
From the picture, it appears to simply connect the inlet manifold to the crankcase via the vent pipe. This vacuum hose defeats the spring & diaphram vacuum regulator in the upper chamber when crankcase vacuum reaches the regulator's limit (lowest pressure / highest vacuum desired) The vacuum hose would continue to route blowby out of the crankcase to the inlet manifold and further increase vacuum (reduce pressure) while the regulator is trying to reduce vacuum in the crankcase. I can't think of a set of circumstances when this would be desirable.
I'm not sure what you mean by the direction of vacuum. Vacuum means that the pressure is lower than atmospheric, it doesn't have a direction. Here, the vacuum hose will have high vacuum (pressure much below atmoshperic) on the inlet manifold end and lower vacuum (pressure a little below atmspheric) at the port into the CCV. Blowby gases will move from the higher pressure area to the lower pressure; from CCV end to the inlet manifold.
FWIW, all the arrows point in the direction that gases in the CCV system move.