I tried a new mixture. I have 2 cups sugar, 1/2 teaspoon yeast... I boiled a little water to dissolve the sugar in, then filled up the bottle the rest of the way with cold water to help cool it... I stirred the yeast up in some warm water and let it breathe for a little bit, then tossed it in the bottle.
12 hours later, I was getting a steady flow through the diffuser once the pressure built up. I wanted to use a lower amount of yeast to make the the mixture last longer, but we'll see how long this goes.
I'm just glad it's working!