Umm... on my system at least, the old breather line from the intake tube to the valve cover was partially metal piping that was attached to another semi-parallel metal tube that was used by the coolant system.

I stole this pic from team integra...



See the red arrow pointing directly at the intake tube (second arrow from left)? On the GS-Rs (This is a type-R, so it's not accurate), that tube that leads from the intake arm to the valve cover is attached to a coolant line. Don't ask me why... that's just the way it was on my car.