Nutloose:
No, no, no.
No air is let back out. In the ASI, total pressure (ie dynamic+static pressure), also known as pitot pressure, is fed to one side of the instrument (ie to the inside of the capsule), static pressure is fed to the other side (ie the instrument case). It's the difference between the two that drives the needle.
That's why there are questions in tech exams such as 'What happens to your IAS if you climb with a blocked static port?', etc.
Any other small hole in the tube (other than possibly a static port in a pitot/static tube such as the PA28's which will have independent tubing to the instrument panel) will be a water drain.
The 'Airpseed Indicator' section here:
http://en.wikipedia.org/wiki/Pitot-static_system explains.
Troy.
I have worded that badly..... what i was trying to get across is that if Pitot becomes blocked the drain will still register static and hence give a zero ASI reading..sorry to confuse you.....but air is let out of it.......... it is factored into the equation, the 152 has the bleed hole on the rear of the pitot head