It's really easy. Just take an empty, clean 2-liter soda bottle and put your solution in there. Then drill a hole in the cap that's a little smaller than the size of your tubing. Force the tubing through the hole (you may need to cut the end of the tubing at an angle and then pull it through with pliers) and it will be tight enough that there will be no leaks of CO2. Then it's up to you how to diffuse the CO2 into the water. You can use a bubble ladder, you can use a fine airstone, you can use a ceramic disk type diffuser, let the bubbles go up into your cannister filter or a powerhead, etc.