I felt the need to write this up due to people thinking that there is only the one way to plumb in and use a catch tank, first it may help some to have a read of this,
which will explain the basics to those that don't already know.
Now the whole reason that a lot of people fit a catch tank is to try and eliminate some of the oil that gets drawn
into the intake system and not only lowers the octane rating of the fuel, (which is undesirable on turbocharged
engines) but also gum up throttle bodies, IC pipes and idle valves etc.
Now the PCV system of most turbo engines consists of a part throttle breather which has a one way valve that
is open during idle and off boost conditions, so the vacuum of the engine can draw any oil vapor thats formed
through engine motion and combustion, into the inlet and is burnt in the combustion process.
This valve is usually plumbed into the plenum, and is vented from the cam covers.
Now as soon as there is positive intake pressure (boost) this valve closes to prevent loss of pressure, and a second breather which is also from the cam cover and has no valve, takes over the breathing, but this is
plumbed into the intake before the turbo, so there is useually only a sufficient depression when there is boost pressure
Hopefully this will give you the general idea of it function, so when it comes to fitting a catch tank, most just
block off the non return valve into the plenum, and then fit an extension pipe to the full throttle breather to the
catch tank, and then leave the other opening vented to atmosphere, which is fine in most cases, and will
achieve the desired effect, however some engines do play up when using this form of venting, but it gets a bit
more involved than i want to go into here.
But there is a second way of achieving the same effect, but still using the factory PCV system with a catch tank,
This basically consists of linking both the full and part throttle breathers together, and running them to the catch tank, then linking the second hose from the tank back to the turbo inlet piping, so the same vacuum is applied through the tank to the cam covers when there is sufficient depression, but in this case the oil vapor is still re emulsified into the tank instead of getting drawn into the intake system, ( it helps to fill the catch tank with stainless scouring pads) to aid oil drop out, and with this method you will tend to see less water accumulation too.
So you see there is more than one way to plumb and use a catch tank.
There is also a way of using the exhaust as a PCV system, which i can go into if anyone is interested.