The CO2 eventually defuses into the tank due to the pressure that builds up in the reactor (2 liter bottle). That's why it takes awhile to start making CO2 bubbles in the tank.
When making your CO2 setup, it is very important that everything is sealed up so the CO2 gets into the tank instead of leaking out where it isn't suppose to. Make sure to make the holes slightly smaller than the width of the tube. Cut the tip of the tube on an angle and put the angled tip into the cap. Then, take tweezers or pliers to pull the rest of the tube through the hole. When the tube is through you can begin to seal any gaps between the cap and tube with the glue.
The check valve is important because you want to prevent water from flowing out of your tank and into the CO2 reactor (and all over you house). Just after you make a yeast mixture, there isn't a lot of pressure since the yeast are just beginning to make the CO2. The the CO2 reactor is like a vacuum right now that will suck the water out of your tank. As long as there is a check valve that has the arrow pointing to the tank
, the water should stay inside the tank.
Another thing to keep in mind is to be careful that the yeast mixture does NOT go into the tank. Some people add another container with water to the CO2 setup. This is to prevent the mixture from going into the tank. Make sure not to tip the reactor over. If the yeast mixture gets into the tube just remove the tube and clean it out at the sink.
Since you are doing diy CO2 and not pressurized you might not want to go buy a CO2 diffusser. I haven't tried any of the glass CO2 diffusers but I have read that they don't work well with diy CO2. An airstone or a chopstick that is positioned under the filter flow may be good enough.
The yeast recipe you are going to use sounds good but you might want a precise measurement of the yeast. Probably 1/8-1/4 teaspoon should be good for 2 liters.
Also, youtube is really great for diy CO2 help.
Good luck ;)