This article shouldn't really be here, there are no air-vents to discuss. They're certainly not in the homeroom, and have very little to do with Twist, Pumpkins or the Midnight Crew.
Such an assumption would be incredibly silly.
"What air vents" is OMG8332 response to "what pumpkin".
In a universe where you count on others to make everything around you it's very common to make mistakes, such as seeing something you shouldn't have, or doing something thats not needed just yet.
When such a thing happens, some respond to mentioning air vents. This is a reference to when, one mysterious day, an air duct system was found for a vampire Gamzee to crawl around and scare people in. The problem was that these air vents could breach the indestructible rooms, so not many were for this idea. As such, the players simply, and lazily, paved it over by pretending there were no air vents after they mysteriously disappear. When asked about these air vents, Gamzee will quickly deny their existence and probably punch you in an attempt to escape the conversation.
In short, 'the air vents' in question, which do not have not and never will exist in the home room, are usually referred to when something needs to be labled as "forgotten about".
...but were there really any air vents to talk about?
Yes, yes there were.