Looks like hose for the 'valve' of the emission control air pump?
Here's my source:
http://www.realoem.com/bmw/partgrp.d...06&hg=11&fg=50
Gonna see right now if I have that thingy, pretty sure I don't
edit: Nope, I don't got one of those...
And, you're correct, no fluid will travel thru that,
my understanding of the system:
When the engine is cold/in warm up mode, the air pump will pump some of the engine's exhaust fumes into the intake of the engine, to warm it up faster/cut down on polution or something.