Originally Posted by Jayhovah

You definitely do not want one that is just an empty can unless you plan to modify it to add something to separate the vapors from the air (since that is the purpose of running a catch can). Almost all the super cheap cans will just be empty cans. The ones mlsully posted are empty, but they come with a little chamber you can fill with something to cause the vapors to condense and gather on.. most commonly people use stainless steel dish scubbing pads (pro tip: you can get them at the dollar store). So this type of can, while empty, can easily be adapted into being functional.

As far as the ones with the breather vents - if you are going to delete the PCV system you would run one of these with the breather vented to atmosphere though the filter... If you are going to add the can into the OEM closed loop PCV, you want one without the breather vent. Some can be configured either way.