nitrous purge is a selanoid that allows you to spray the nitrous into the air instead of your engine. the reason for it is to clean out your nitrous lines. i have to go to work otherwise i would explain it a little better but if you want to look on one of the nitrous companies websites you should find a good explanation

It didn't cost anywhere near $100 though. I ended up going through the cowl. It'll purge over my roof now.