Used to do a little home brewing.
Once you build up the alcohol level to about 3 or 4% then the yeast starts to die (Thats why most beers are at that level). Same yeast used to make bread rise.
Some stronger yeasts are available that will tolerate higher alcohol (many found naturally on grape skins so wines can get to 8%)
Barley is full of starch - so we wet it, let it start to grow and sprout, the growing plant needs energy so it begins to break the starch down into simple sugars (this is malt)
Traditionally water was boiled to kill any germs that might compete with the yeast and it was poured over the malt where it disolved the sugars and starches out better.
let it cool to blood temperature before adding the yeast.
Rather than a leak - it could be you're being too kind to the yeast - if you keep it nice and warm and give it lots of simple sugar then it will go into 'party' mode, froth lots, produce CO2
and alcohol and reach a level at which it kills itself quickly.
I had a demi-john (Glass one gallon) which 3/4 full would ferment in a cool room for months. Used a little water filled swan neck air-lock so the CO2
would escape but bacteria couldnt enter. would bubble once per 5 - 10 seconds.
Perhaps you could kill two birds with one stone - get a nice homebrew wine kit and that'll sort the CO2
production and you'll get a nice vintage at the end.
You might need a longer tube to move the fermenter away from the nice warm tank area - dont worry about needing special CO2
tubing - it's a very heavy/dense gas and you have no real pressure - standard aquarium tube will be fine.