Stock PCV depressurizes the crankcase and at the same time separates oily mist into oil and air, but not entirely and because the modern engine normatives do not allow engines to produce waste (catching oil in the OCC), the oily air takes another circle through the intake into the combustion process. This is where we get to a problem we are addressing with OCC - sludge and carbon build up in the engine internals. With aftermarket mods - OCC, we can now improve the separation of oil and air and prevent oily mist to go through combustion process. We extend the path the oil needs to take, increase the time it has to cool down and condense, and therefore turn in to oil and air. The intake in to the OCC is lower AN fitting and outlet is upper AN fitting, in-between is a filter, even further reducing a chance for an oil to pass through, on top of that OCC's are higher than PCV to even further reduce the chance of oil getting into the intake for a combustion again. It is called an OCC (oil catch can), but you are actually catching misty oil vapors that separate in to oil and air, or more precisely in the OCC bottom tank, you will be catching mixed dirty oil and water.
The time which will take for OCC to fill depends on driving conditions. Left OCC (looking from rear towards front) keeps the crankcase vented while the engine is under light load, or steady throttle (vacuum). Once the boost steps in, the NRV (non return valve) closes and right OCC takes over the job until there is boost in the intake manifold. As soon as you step off the gas pedal, the vacuum is generated again in the intake manifold and the left OCC takes the job over again. Street and lightly driven cars will fill up left OCC sooner than right. Track cars will fill up right OCC sooner than left but they are not under boost all the time, so left OCC will fill up too.
Venting straight in to the air thorough a breather filter is an option if you don't mind greasy engine bay and oily smell behind you. Perhaps better would be to route that in to the exhaust system and let it burn, but not the most elegant solution for a car like 4C, once again smelly.
