It is stock on 96 and newer hummers. The labor time doing a normal pressure test on the van/hummer with the annoying intake manifold was so bad they attempted this. Idk they kept using them because by 1998 the protocol came out to not use it. They are on the wif line side which is pre filter and on its way to the drain.
I don’t remember the proper name for them. They are a waste to use because of the deteriorating rubber line after the fitting even is someone moves it inline to the ip inlet.