HI Snaken,
A question why do you have a return back to the sump?
I assumed an
oil catch can is there for when the engine is in trouble and pumps the
oil into the rockers. I will have to check but I think Cams require a can the same capacity as your engine, eg a 5lter requires a 5lter catch can.
In my engine I have a 7 ltr can and after a few months get a small amount of condensed vapour in the can that I drain and that is it.
Phil