It does the exact same thing as a catch can, but it still keeps the smog system legal does not foul the airfilter and used to cost about 7 bucks has no filter in it just course steelwool. It's what I would use on a YJ. Also you can also run the vent hose into the the tube that goes from the filter box to the intake that way it happily slobbers the fumes but doesn't foul up the airfilter. That is basically what Chrysler did with the 2.4l engine