How do you know if it works????

 

there should be a slight vacuum in the system, the popular test (however not accurate) is to take off the oil fill cap and put a rubber glove on it, it should kind of sort of suck in slightly. if it inflates that's bad and if it does nothing its questionable. same with the oil dipstick tube.
there is some testing equipment you can get to get an accurate measurement but I think for the most part the glove thing is alright. when i did mine it went from blowing smoke to sucking a length of string in so i knew it was at least close to perfect numbers.

but remember if those two hoses are crossed then you will more than likely be sucking up oil into your intake manifold, not much but you would see an increase in oil consumption. it might work fine with the vacuum in the system even if its crossed but keep an eye on your oil.

 

very interesting cross section. I had been meaning to cut a clogged one in half but never fired up the saw.

Studying that picture it looks as though there would not be a reveres in pressure if the hoses are switched, but a very short life for the oil catch because of the direction of flow -- like putting a one way only fuel filter on backward. Lasts only a couple thousand miles.

I have redone several PCV systems because the hoses were reversed.

 

that cross section is a bit exaggerated but its the general idea, its quite simple in how it works really, its amazing that they go bad so quickly.