Fresh2o
Aquarium Advice Addict
Well i just made a single hole in the top of the 2 litre bottle (edit) in the lid so you can remove the tube to mix the yeast sugar and water. if you make it small enough that the tubing is a tight squeeze and you have to drag it through, most of the sealing is already done for you. I have a hot glue gun that i use as insurance. A light seal on both the inside of the bottle top and outside and it is good to go. you can also cut the tube and apply a valve that you can switch off to refresh the bottle. Good luck if you try it. it is very simple really. Get the seal right and you have a cheap CO2 source that shouldn't ever suffocate your fish. I have run three bottles at once to try and clear algae and the fish seemed fine for the fortnight i had three bottles running.
Ditto. I've had good luck with a leak free seal using a 3/8" hole and silicone airline tubing. If you cut the end of the airline tubing at sharp angle, you can feed the tip through the hole in the lid and then use needle nose pliers to pull it through..