Excerpt taken from http://franksseptic.com/
"Septic Do’s and Don’ts: Don’t add yeast, baking soda, store bought septic chemicals, and bleach. The natural bacteria in your tank lives at a certain pH level. The bacteria eats waste and it is separated into water and solids. If you change the pH level of the bacteria it will die, and will not separate the water and solids and your tank will fill up and also produce a septic smell. Yeast does not provide the needed bacteria in your tank. It simply ferments what is in there. Baking soda changes the pH level in the tank, thereby killing the bacteria. Store bought septic chemicals can also change the pH level and do not provide “live bacteria” to your tank. Bleach can change the pH level if used in large quantities, used sparingly, it will not affect the bacteria. If there is no bacteria left in your tank, Frank’s Septic does sell “live bacteria” which can be added to your tank and start the organic process of breaking down the solids."
Hope that Helps!