Crankcase vent needed?

[Arctic RX]

I noticed a crankcase vent being mentioned in a few posts. Can someone please tell me how to do this and/or why it is needed. I'm assuming it is to reduce some pressure building up in the crankcase?

Bone stock RX-1 2003.

Thanks in advance for your help, :?

 

[POWERHAULIC]

You have one, it is the hose on the left side of the air cleaner

 

[DYNAREX]

if your airbox is stock dont worry
if you are running ecp filters you need my crankcase evac kit
there are lots of post about it in the general forum

 

[Arctic RX]

Thanks, do you sell the ECP filters DYNAREX :?: