I use a 2 liter bottle adding 1Tbsp yeast activated in 1 cup of water at 100 degrees and 1 tbsp sugar to 2 cups sugar. Fill the bottle to 2/3rds full. Once the mixture starts to decrease in production, I simply syphone off some water and add another cup of sugar. This only works about 3 times but there is never a stop in production this way. It takes about 3 months for my bottles to kill the yeast and completely stop production. No baking soda, plain bakers yeast and nothing else added. Produces for about 4 weeks at a times on the intital setup then 2-3 weeks after each time I add sugar. I have even had really good results by letting the yeast settle out then draining the water down to about half a cup and adding a new water sugar mixture. This way makes a huge amount of CO2 but uses up the sugar much faster because of the large amounts of yeast that build up.