After looking online, I found this: http://forum.northernbrewer.com/viewtopic.php?f=3&t=61167&sid=f054f78a221afd9740f0c31521c11bc4 , which really helped me with the basics and why not to use brass/copper. His design is pretty great, but I think I have been able to simplify and make it cheaper.
Step 1: Gather needed materials
2 1/2" threaded to 1/4" push to connect
1 1/4" to 1/4" push to connect
1 1/2" threaded to 1/2" barbed fitting
1 1/2" Brass Tee
Some 1/4" Ice maker tubing
1' Length of vinyl tubing (not pictured)
I think I spent just around $25 on parts (if that much).
You are a going to need a drill, 1/4" bit and an adjustable wrench
Step 2: Drill out one of the 1/2" threaded to 1/4" push to connect
Flip it, so the threads are facing up and look for the hole on the inside, you need to open that hole to 1/4 inch. Its at maybe an 1/8" or 3/16".
Keep in mind there is an o-ring in there that has to stay intact.
If you do this right, you can now pass the 1/4" tubing through there and maintain an airtight seal.