Rich is right.
I would add the following as notes of interest.
1. Make sure the opennings in the valve covers are baffled. And MAKE sure they are properly baffled. You will puff blue smoke if the baffle is not good.
2. Use the correct PCV valve. I had one that puffed after I fixed small baffles and went to the recommended one for a 1971 Boss and the puffing went away.
3. Use the air cleaner as the vent if you can. What I have found is that
oil at hi RPMs splashes and/or vaporizes and goes out the vent/breather/hole. I found that when the tube was connected to the air cleaner, the
oil went up the tube a bit, but it never made it to the inside of the air cleaner. When using a push in breather, I got drips on the valve cover(s).
4. Use a Vac. gage to see what you have going on with the manifold vacuum. I found that I could reduce the tube size for the vent and get rid of residual
oil from the valve cover openning.
Here is what you want to do: By putting this system on your engine, you want to pull the blow-by gasses ( gasses that get past the rings into the crank case ) from the crank case and burn them in the combustion chamber. Since one side is vaccumming the air out, you will need to provide a source of air, hence a vent/breather/connection to air cleaner.
I hope this helps.