Now I'm even more curious than I was when I first looked at the photo.
Having looked at hundreds of kitchen sink set ups, I had never seen anything like that so-called vent pipe. Of course, I've only looked at sinks in my area. It looks like venting of some sort but for the drain? Are you sure? The disposal drains through the large white pipe running to the right of the photo and should connect into the main drain system. The location of the vent pipe doesn't seem like it would be venting for the drain.
I'd love to see a photo of the rest of the under sink area to see how that vent piping connects to something!
