I owned a skyline that I ran a catch can on and I just vented it to atmosphere, through a small filter which I'm pretty sure made it legal. The main reasons I vented to atmosphere for is 1. sometimes the catch can won't catch everything and this oil vapour mixed can cause detonation and when plumbed in before the intercooler or turbo, can sometimes accumulate in the intercooler itself, 2. (this one depends on where its plumbed in also) if or when for some, your engine lets go under boost the blowby will pretty much push a sh1tload of oil out the breather and go into the turbo\intercooler\engine and cause more drama(bend tubo blades etc). I vented mine to atmosphere to hopefully avoid some of this. It is important though when running a vent to atmosphere setup that after the catch can a filter of some type is used as when the engine is under vacuume it will be sucking a small amount of air in also and you don't want crap getting in with your cams. Keeps the cops happy too. RB engine is a bit different but the same principles are still there. If anyone wants a pic I could probably put a couple up. If I am wrong by the way, I am happy to be corrected! My 2c Smitty