1 tsp of active bakers yeast to 2 cups of sugar. poor contents into a 2 liter. Add water warm enough to melt the sugar, mix well then finish filling with warm water, leaving about 4 inches from the top of the bottle empty. You should be in full production in a few hrs. drill a hole in the cap just large enough for fish tank tubing to run through. Then put the other end of the tubing in the box you intend on gassing with.