Aquarium silicone is what I used, I stuck the hose through to the inside section of the cap a little longer then I wanted it to be, globed some silicone around and pulled the hose to where I wanted, then put silicone on the outside.
Also brown sugar is fine, I used it in my first batch. I have since moved on to the cheapest sugar I can buy and I do 2 cups sugar, 1/4 tsp baking soda, 1/4 cup cornstartch, 2 cups boiling water in the 2L bottle, cap it off, shake it up, and let it cool down to just above room temp. About 15min before its to where I want it I mix a little sugar,water, with a tsp of yeast and let the yeast activate before pouring it into the bottle. The starch turned the mix into a thick sludge but 3 weeks later I have yet to see much of a drop off in bps from that bottle. Keep in mind this is a dual 2L setup for a 55g so even a single 2L might gas your fish.