I had a septic tank many years ago and used Rid-X. The idea of Rid-X is that it contains enzymes and bacteria that help break down wastes in the septic tank. That should allow you to have it pumped out less often. Internet message boards suggest using buttermilk and/or baking yeast combined with a little sugar to feed the yeast, each month, instead of Rid-X.
On the other hand, both the Tightwad Gazette and the University of Minnesota Water Resources Center say that yeast and Rid-X don’t do anything and are a waste of money. They both say to have tank pumped every 3–4 years. The septic tank will ferment best if you don’t use a lot of bleach. It’s best to avoid antibacterial cleaners and non-biodegradable detergents. These products kill the bacteria that are needed to break down wastes in the septic tank. The tank naturally gets bacteria from the human waste flushed into it. Using garbage disposals, taking very long showers and otherwise using lots of water will overwhelm the septic system faster than if you use less water.