On Thu, 24 May 2012 21:27:56 +0000 (UTC), "Arklin K."
wrote:

The interior vent allow air that gets in from other sources to get out.
In a perfect world you wouldn't ever get air in the system but it
happens (hooking up the vacuum etc).

Ah, I see. I guess it lets air go to the top instead of collecting in the
bottom (I guess).

Close... The screen on the tube stops material from the tank that
will clog the vent. Pressure release...