I recently bought a new return line and inspecting it closely I found out how to appropriately and easily disconnect it. I am talking about that oil return line from oil return tube on metal valve cover N52's (US 2006 330 and 325s).
It is meant to be disconnected by a fuel/ac quick disconnect. Any push, pull, press etc from outside on those tabs won't do anything to unlock it. It is not designed that way. Those four tabs are meant to be spread out from inside for unlocking and this is done with a line quick disconnect tool. I didn't have any, so I visited and bought a cheap plastic set from closest Autozone:
http://www.autozone.com/test-scan-an...?checkfit=true
Updated: At the below video I used the 5/8 inch blue tool from the Autozone set but had clipped off some part of it so that it would fit. Upon one more try later on, I found out that actually the 1/2 inch red tool from same set works perfectly fine and is the correct size to use. Once the tool is inserted good, you just pull the tube out. It needs some force but not a lot. A higher quality metal tool would probably work better and last longer, but this plastic set gets the job done especially for once or twice use.
Here is a video of it, sorry for the lousy camera work: