Before I switched to vac pump I ran hoses from valve cover breathers to oil separators/catch cans then out to the headers. It's amazing how much junk they actually accumulated. Mostly condensation/alcohol as I run E85. I still use them with the vac pump and they keep a lot of junk from going through it. What I read was the water and alcohol that goes through them is what messes up the seals the most. The oil helps keep them lubed. It just so happens that it seems the catch cans catch mostly water and still let oil pass as I get a few drops out of my pressure adjusting valve. I have it inline instead of in a valve cover to keep from pulling dirt into the engine. I still get a little water/condensation in the can/breather after the pump but the cans catch A LOT!