I want to add that if you drill the hole smaller than the tubing that you don't have to use the sealant. I have made at least two dozen DIY bottles over the years and have never had to seal a single one. And I do the same with my DIY bubble counters.
Also the use of juice bottles is much better than soda bottles as juice bottles are less likely to fall over. And if you can get beer or wine yeast it's much better for long term production of CO2 than bread yeast is. I also use the jello method and a 2 liter bottle will produce CO2 for around 4 weeks.