Brewers yeast, sugar, a two liter pop bottle with a hole drilled in the top of the cap. Shake every few hours.
The brewer's yeast and sugar recipe is pointless. You'll spend too much time and money managing it when all you really need is an intake and exhaust fan which will supply your girls with all the CO2 that they need. Don't make the growing process more complicated.
What would be the source of CO2? The levels of CO2 in outside air are far lower than the optimum levels for a plant grown indoor.
The normal concentration of CO2 in the air is around 300 PPM. That has worked just fine for the last 4 billion years and is more than enough to produce 1 gram per watt per 2 month period.
Sure, it will be "just fine", but it by no means is optimal. I'm pretty sure that the author of the thread was looking for ways to improve upon the basic levels of CO2 that we find in the air that we breath.
He's probably looking to increase CO2 levels because he heard that it can increase yields by 20%. The caveat is that you should have everything else dialed in before you look to add additional CO2. And considering he's asking about a janky prison wine set up, that tells me that there are other things he could be doing to increase his yields.
That we can agree upon.
If you're not trying to increase your yield, what exactly are you trying to accomplish then? CO2 enrichment helps in 2 main areas if done properly. 1) It will increase your yield. 2) It will speed up flowering time (increasing your yield). This is of course assuming that you have your temps and realtive humidity dialed in .............. other wise, you're just wasting your time, and could in fact damage/kill your plants.