With mine (LSA Conversion), I have mine pulling from the valley cover. My driver's side is not on the catch can.
I thought the 'dirty' part was coming from the Valley Cover -- never have had any oil build up:
Passenger and Drivers valve cover vents linked:
Linked to Air intake:
I've never had a problem with it this way -- but I also have a vented Catch Can and
Breather on the passengers valve cover:
-Don