Like roving beetle said, it is better to keep a slight negative pressure in the engine. The set up I have allows fresh air to be drawn in to equalize the engine. Doesn't work that great because the air filter can doesn't really draw that much vacuum on the small hose from the driver side valve cover gasket. It is not the best solution but better than simply putting breathers on both valve covers. Ideally you want a breather on one valve cover, then the other valve cover going to a catch can then to ported vacuum (I.e. throttle body) HOWEVER since we have EFI any air consumed after the air mass meter will throw a CEL due to extra oxygen reacting with the front oxygen sensors, or a commonly known as a vacuum leak. So porting vacuum gets tricky.
The set up on our engines is similar to Mercedes Benz 112 and 113 engines. They have what is called partial load and full load breathers, in other words one breather connects to manifold vacuum and the other connects to port vacuum...therefore it is theoretically removing blow by gasses equally at low rpm and wide open high rpm. Blow by gasses are higher during wide open high rpm, therefore you need to port the breather to better evacuate the gasses.
At the end of the day the set up BMW has used is great, due to the PCV being routed into each of the intake runners....the downside is when one of the breathers fail it directs oil straight into the intake runners at idle, locking the engine up. Seen that several times.
There is a fine line, creating excessive negative pressure eventually results in leaky rear mains or other seals. In other words if there is too much vacuum in the engine fresh air has to be pulled in somewhere, and its usually the weakest seal. It's like a windshield washer bottle....if it is completely air tight, then you will notice washer fluid being 'pulled' out of the washer nozzles when you're driving down the road. Or the better example being, fill a plastic container full of really hot water, then pour it out quickly, the bottle collapses....even with a tiny vent hole. The bigger the vent hole the better the bottle will equalize.
No matter how you route the breathers right now, it is way better than the current set up, from the stand point of keeping the blow by gasses, oil, water, etc out of the top end. Keeping the proper weight oil in your truck, at higher temps helps boil the water into vapor, then you just need to come up with a solution to properly evacuate it out of the engine.
Believe it or not a lot of the drag racers actually bolt a belt driven vacuum pump to draw the excess pressure out of the engine, applications that see excessive blow by due to high rpm and low tolerance rings (theory being loose rings will expand under high load and high engine temps.)
just be carefull with water crossings not to suck up water into the engine.
