Planted Tank Guru
Join Date: Jun 2004
Location: Baton Rouge, LA
1) Bottle caps are made of polyethylene, which (without some exotic techniques) cannot be glued. If it's not leaking now, it WILL leak later! The simplest way to get a reliable and long-lasting tubing connection is to drill a hole slightly smaller than the tubing, cut the tubing at an angle, and pull it through. However, your existing cap can be salvaged. Remove all glue, push the tubing through the hole, and shove a tubing coupler (or similar, like a plastic part from an airstone) from the inside of the cap into the tubing, expanding it into a snug fit.
2) The only time I've ever tried 1/4 tsp. of yeast, it failed to produce CO2. Sugar water does not provide all necessary nutrients for life. Yeast live in it only by recycling a limited nutrient supply from their own dead in an endless loop - that's why the max population (and CO2 production) tops out at an amount determined by how much yeast you add, rather than constantly increasing until the sugar is gone. With such a small amount of yeast, the nutrients may just be too sparse and diluted, leading to a "stall". You might try adding more yeast.
3) I use Fleishmann's "Active Dry" and lukewarm (body temperature) water. Only two failures - one described above, one when I skipped shaking the bottle. Anything fancier, including use of Prime or "proofing" the yeast, has proven completely unnecessary; although addition of 1 tsp. of baking soda does seem to extend production time slightly.
4) In a 2L bottle, bread yeast will die of alcohol poisoning before they can convert 2 cups of sugar. They're good for 1.25 cups guaranteed, 1.5 cups at best. Anything more is wasted sugar.