Your right TRM. Percs are supposed to be a closed system. It works by splitting the air/bubbles up in different ways and patterns using pressure. Having inward pressure on a closed system makes it a straw. A tree perc may bubble and fizzle when pressure is used inwardly, but only at low water levels. However, it isnt Actually filtering it. Air will always take the path of least resistance. So just how it was held in that picture, one or two slits on the tree may allow alittle some of the vapor through. However that isnt filtering. And may fizzle and bubble. And if you check the wording, when vapor "fills it". well the upper chamber will never fill by itself, unless there a leak in the system (i.e. exposed slit). Try blowing the male joint (no pun) end and see what happens. Will bubble right up to the top. Set it on a table flat and all slits covered by water. In a correct system.
And for all intents and purposes, David Goldstein FTW.
G must be having a great day. He said testing starts this week, so sure as shit hes having a grand ol' time.