It isn't in line with the inlets. The two inlets "dump" into the catch container. The breather is attached at the top.

And you don't want a closed unit. You need to let the escaped crank case pressure vent somewhere. If it goes into a closed container, I imagine it may possibly cause a mess. This is why most PCV systems either recirculate back into the intake manifold, or back in the old days it just dumped via a dump tube onto the ground. According to Tony, his new diesel Chevy truck still use this dump system.

I imagine you could use a closed system where the catch can scrubs the vaporized oil out of the air and the pressure is allowed to vent back into the intake manifold, but that still isn't a foolproof means of keeping oil buildup out of the mani.