Obtain the following:
1 - 2 liter bottle clean and empty
1 - Airline Check Valve
2 - cups sugar
6 - cups warm water (approximately 100 degrees. plus or minus 5 degrees)
1/4 - tsp bread or active dry yeast (red star, fleishcmanns, etc)
1 - ft length of silicon or rigid plastic tubing
X - length of same tubing as above long enough to go from bottle up and into tank.
1 - airstone - These come in different types wood, rock/stone, or synthetic micro bubbler.  The synthetic works best and lasts longer exposed to the CO2.  The rock/stone works better then the wood but will crumble apart after a few months.