Yes, removing the intake in a 6 cylinder BMW is a pain in the ass (or so my dad, the 325 owner) has told me.
The spring loaded tube must be (I haven't seen my father's engine though, but every car engine has one somewhere) the PCV valve, which is a one-way valve (that's why it's equipped with a spring loaded plunger) that relieves pressure from inside the crankcase to the intake manifold. It happens that no matter how good your compression is, some gas escapes through the piston rings to the crankcase and starts building up pressure inside. The PCV valve relieves that pressure, and the spring loaded plunger avoids intake air going into the crankcase.
Another job of the PCV is to reduce moisture inside the crankcase. The combustion gases are rich in water vapour which would contaminate the oil if not vented through the PCV (which by the way means Positive Cranckase Ventilation)
Hope it is of help.