Actually there shouldnt be any air in the rad or your system loop at all.
Use the T connection to access your system and for more water volume.
The T connection in my system is the same height as the barbs on the rad. The T connection is below my waterblock. Works just fine.
I would make sure T connection is on the same water line as going into your pump.
Here's a pic:
http://www.chadandjodi.com/watercool/newwater.jpg
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