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

I'm using 1" pipe and 1 1/2" on my stand pipes.

 

What size hole for the drain?

 

1"

 

So, are you going from 1" drain, splitting into 2 1/2"?

 

No, it's 1" splitting to two 1"

 

I've been using that configuration for about 6 months and have had no trouble with it. A few good sized snails have made it to the sump no problem. Just a little noisey when they are going through.

 

You have one going straight down, and one T'd off to the fuge? And it's not flowing over and down, only down.......Hhhmmmmmmmm;
You have some good advice, and the comment about the path of least resistance- ( I path I rarely take in life btw)
Surely you're not trying to change the laws of hydrodynamics?

 

No, there are two 90s above the left overflow.

 

I'm having a little trouble understanding your drain configuration. From the drain line from the tank, is there a "t" or something else?

 

T. Above the T are 2 90s to get the water into the sump.