On Sat, 26 May 2012 12:19:25 -0400, gfretwell wrote:

The air will tend to collect in the top of the tank, the vent allows it
to escape and go on out to the pool.

Oh. Hmmm... I guess the air that collects at the top of the tank gets
sucked from the filter screen at top, down into the thin pipe, into the
bottom of the filter, where it then flows back out to the pool.

Interesting setup! Thanks for explaining it!