Originally Posted by dantodd
I do this all the time. Buy the bag in box (BIB) where ever you find them. They aren't supposed to sell to you unless you have a coke contract but most stores don't care. You'll have to "fix" the BIB valve to flow free. Then you measure out the correct amount of syrup for a 5 gallon batch and mix it in with water to fill your corney. I put it on 35-40 PSI and use a picnic faucet. About 15' of tubing keeps me balanced at 40 degrees. I don't recall the exact amount of syrup I now have a gallon jug marked with the amounts to put in. I think you want about a 5:1 ratio, but since it's your diet coke you can mix it however you like.
If you can get some BIB syrup, you can mix it yourself if you have some cornies!
I think Sam's and Costco sell BIB's, but you might pay a little more!
Another idea is to become good friends with a local restuarant and see if they can order some extra BIB's that you can purchase off of them!