what you mean?
any catch can is good if it has 2 chambers, because in theory the rocker cover inlet is going to pump dirty air into the can, and if there is only a main chamber with no wall separating the inlet and outlet, the dirty air is just going to be sucked strait into the other hole outlet, and the dirty air stays dirty when it goes back into your intake, if there are 2 chambers, the dirty air from the rocker covers will hit the 1st chamber wall and the oil and muck will stick to it and the air will then continue to flow into the second chamber and continue its cycle.
but, there is a way around this if you only have one chamber (and its what i personally have set up) and thats packing steel wool into your catch can, not the fine wool, the large strand steel wool, the steel wool acts like the chamber wall and the oil will stick to the steel wool letting the cleaner air continue through it. if you use the finer steel wool then particles of steel may continue into your engine (i forget the names of both the wool)
use this stuff
not this stuff