Here's the Dale Clark trick -
Everyone's right, that extra hose is the vent for the airpump air. The ACV routes air from the air pump - some times, there's extra air that's not needed. If so, the ACV dumps the air to "relief", which is just the extra air. Unfortunately, this makes a rather obnoxious "mooing" sound.
After some experiments, I found a killer solution to the moo. Go to Wal-Mart, and buy a 7/8" black rubber chair foot. They're designed to go over a dowel at the bottom of a stool or the like, and kind of look like the rubber bottom for a crutch or something. It will fit PERFECTLY on that nipple up by the intake manifold.
Now, take your chair foot and drill 5 small holes in it to let the air out. Put it on with a hose clamp. Done. Looks clean, gets rid of ALL the moo, and you don't have goofy plumbing running across your engine bay. I've been running mine for some time now with no problems. I'm slowly testing different intake ideas looking for the best, clean solution to things