Just seen the tags in this thread that I'd missed yesterday, sorry chaps.
Stuart: the 30psi you're seeing is HOPEFULLY boost + atmosph, so take away 1 bar and you're left with just over 1 bar of boost, which is closer to the truth. The MAP sensor also cannot read 30psi of boost, so it MUST be absolute pressure.
The idea of the TIP return is that the TIP is usually under a very light vacuum due to the restriction at the air filter. It's not a huge vacuum like the inlet manifold, but it is at least a negative pressure.
it's thought that this negative pressure will help to draw the crank case gasses out of the block, rather than the block simply venting itself to atmosphere.
i tried running my new catch can setup vented to atmopshere, but after around 6-- miles or so there was a heavy build up of emulsification in the crank and cam cover breather lines, and the can was collecting the nasty gunk too. You could also see the breather filter smoking when the car was run on the dyno:
This was the inlet to the can after 600 miles:
Pretty nasty.
Firstly I returned the catch can to the TIP with a 25mm line:
Then I added a T into the main crank breather near the source, to draw direct from the crank case as Alex alluded to:
Pretty hard to make out, but it's a 10mm line that runs from the OE plenum PCV take off, via a check valve, down to the main crank case breather line. This draws the crank case gasses out on over run when the throttle plate is closed, and it does a REALLY good job because there is a very strong vacuum in the plenum.
To give you an idea, the vacuum at the plenum is strong enough, that not only does it draw sufficiently from the crank case, but it also creates a vacuum at the catch can and draws any gasses out of the catch can too:
After just 50 miles with the PCV stuff, the can inlet had near on cleaned itself fully:
And now after a few hundred miles more, the can is 100% empty, and the pipes are spotless inside like brand new.
To all intents and purposes, it seems that it is now a totally self maintaining system.
I realise this goes TOTALLY against the standard ASN route of 'rip it all out it's ****'. I believe that all the stock pipework is most probably fit for the bin on any used 1.8T that's ever been sold, but when new and in good condition, it seems to be a system that works well.