Sugar, water and yeast produce alcohol. You better watch out for the federal police, they don't like illegal distilleries.
If you use a bigger bottle and a wine/ spirit yeast instead of bakers yeast, you will get more gas for longer.
You can buy 20-40 litre plastic water containers from hardware stores or chain stores like Bunnings, Kmart, BigW, Target, or even camping stores. You drill a small hole in the lid and put a rubber grommet with a bubbler (available from beer brewing stores or online) in the lid. Then attach some plastic hose to that and run it to the tank.
Fil the container with dechlorinate water and add a heap of sugar. Any type of sugar works and you can also use molasses or fruit. Add some wine or spirit yeast. These types of yeast are available from brewing supply stores and can tolerate a much higher level of alcohol in the water before they die. This means they keep producing CO2 for longer. After adding these items, put the lid on and do it up tight so no air leaks out. Leave it to grow. A decent sized container can produce CO2 gas for up to a month.
You can collect the CO2 gas in balloons. You just need to attach a balloon to the outlet of the container and let the balloon fill up naturally. The hardest part is stopping the balloon popping off when it starts to expand. Swimming pool toys that float, and air mattresses can also be used to hold excess CO2 and most of these have a one way valve to stop air leaking out.
Be careful using air mattresses because some have a power in them to stop the plastic sticking. Cheap floating pool toys don't usually have anything in them.
