WUC555

I need to install 2 catch cans on my car. It's a MY00 GC8 ej207. I understand 1 of them needs to be put in position 5 in the picture. However the research I've done advises to place the 2nd catch can in position 6. From my understanding though, that would mean that the dirty vapour gasses from the crank would return back to the manifold when the PCV valve is open. So I'm thinking it would be better to install the 2nd catch can in position 7. Would the best place to install the second catch can be position 7? Any advice is appreciated. Thanks