I will give you a quick rundown of what I did when I ran DIY CO2. There are 80 bazillion recipes out there and all of them are only slightly different. Here are my thoughts:
Yeast needs to be warm - if your room is below 70f, you're going to have to use a LOT more yeast to get the desired amount of CO2. Some people put heating pads (the kind you use for muscle pain) under/around/close to the bottle(s) to get the temp into the mid-70s to 80f....BE CAREFUL THAT YOU DON'T OVERHEAT THE BOTTLES OR YOU WILL HAVE A SERIOUS MESS ON YOUR HANDS!
If you can think of a better way to regulate temp, use it.
Recipe I used:
2 cups sugar, one of which was dark brown sugar.
1/2 TSP Fleishmann's Yeast (NOT QUICK ACTING)
1/2 TSP Baking Soda
~2 liters of tap water (I used an Arizona Tea bottle which is 1 gallon capacity)
I filled the bottle with the hottest tap water out of the sink. Do NOT overfill the bottle. Go right to the part of the bottle where it begins to curve toward the top, assuming you're using a 2 liter soda bottle. Fuller than that and you risk drawing liquid up the airline hose, and you definitely don't want to do that. Ok, I added my sugars and shook till dissolved. Then I took a cup OF THAT WATER and added the yeast to it and sloshed it around to wet it. I let this mixture sit for maybe half an hour. This is an important step! Once I saw that the yeast was foaming I poured it into the bottle, which by then had cooled off to about 100f. This produced the most consistent CO2 output of any recipe I used. About 2 weeks worth of gas... If you cap off the bottle of CO2 mixture before the yeast has a chance to grow a bit it seems to stunt it and you (I) never seem to get full productivity out of it.
The other thing I noticed in your pic is that you scotch-taped the airline into the cap of the bottle. That won't work. You need to drill a hole in the cap that's undersized for the airline you're using, and then take and cut the airline end at an angle so that you can grip it and pull it through the hole in the cap with a pair of pliers. This will create an air-tight junction. Glue won't stick to the airline or the cap, so this has proven to be the best method.
Make sure it is a TIGHT fit. You also need a check valve between the bottle and the aquarium. You don't want CO2 mix in your tank.
One last thought: That bottle you're using looks like plastic. Those jars are not thick enough to handle the pressures you're going to be generating and I would definitely re-think using them. Pop bottles are designed to withstand high pressures from shipping and general handling and are a much wiser choice here. The only downside they have is that they tip over easily. Make sure you provide for that possibility in your setup. I used the Arizona bottles because they're thick walled and they were handy at the time. I didn't use them with any diffuser that caused back pressure like you say you won in your auction. Those are generally a PITA with DIY for various reasons. YMMV.