I put a T on my overflow, water won't go to refugium

I say, dump the Tee.... You seem to be trying to make water turn 90° when it's heading straight down? That's tough in any situation...

I'd go looking for a wye, maybe a 45° street fitting that goes into a true union ball valve (I think gates are overrated) and leave your main drain unobstructed, no ball valve needed on the main drain.

Just to give you an idea of the different ways you could go abouts this.
http://flexpvc.com/indexWyes.shtml

 

Those 90's just change the direction/slow the flow some; but are still linear and don't make a difference on the flow to the fuge.
Put a valve after the T going to the side with flow. That will divert some pressure/fluid to the fuge side.

JUst make sure one pipe will handle all the drain flow, or a spill over may occur.