For the airline into the bottle(s) simply drill a 13/64ths inch hole through the lid, cut the
silicon air hose at an 45 degree angle, push the point through the hole in the lid, use pliers if necessary to pull the hose through the lid 1/2 inch. No GE silicone, no mess, fast and easy (thanks
Rex Grigg).
For my DIY on my 50 gallon I can lower my pH from 7.6 down to 6.6 using a bubble ladder from aquatic magic (Hagen makes on as well). I will be switching to pressurized CO2 at my earliest convenience since the fluctuations in gas/nutrient levels appear to promote algae growth. It works but it takes a lot of work. I used the 2 cups sugar, 1 tsp yeast, 1 tsp baking powder (or soda). I found the 1/4 tsp recipe was didn't work for me but my recipe burns out fairly quick - 6-10 days.
Regarding yeast, it is a living organism and hot water above about 104 degrees will likely kill it. I always dissolve the sugar and baking powder first by shaking vigorously then after adding the yeast I simply gently circling the bottle on a counter top.
If you want a great CO2 diffuser search Google for "niko hagen elite co2 diy" and you will find a long thread describing using the Hagen Mini Elite filter as a great CO2 diffuser. It may be too effective for smaller tanks.
Check valves are a great way to change out bottles on multiple bottle systems.
Reading this thread made me realize that the white filmy gunk that grows in the bottom of my bubble ladder is probably yeast fed bacteria. I will be adding a bubble counter (aka gas exchange bottle) before feeding the CO2 into the tank to hopefully prevent this.