I know this topic has been thrashed to death on TBN/CBN and I am not doing this to upset anyone with "faith" in their favorite "spunk water", yeast, magic powders, or cabalistic chants BUT...

Here is an excerpt from the March Popular Merchanics:

Septic Tank Additives.
Our new home has a septic tank and a drain field. Is it a good idea to use a flushable additive to treat the septic system, or is it a waste (no pun intended)?
FRED MILLER, BLAIRSVILLE, GA

There are approximately 1200 chemical and biological additives for use in septic systems on the market today: According to the claims in their promotional literature, they are supposed to improve the operation of the septic system and, in some cases, eliminate the need to have the tank pumped. Most of the manufacturers' claims have not been subjected to controlled scientific tests with field data replicated by third-party researchers. In cases where studies have been conducted, there is some debate as to the additives' effectiveness.
Washington State’s Department, of Health invited all manufacturers to provide evidence from controlled studies that demonstrate positive benefit to septic system performance. None were submitted. Also, according to a document from the North Carolina Cooperative Extension Service, additives do not reduce the need for regular pumping of the septic tank. Furthermore, the document says, some of the additives contain organic chemicals that may damage the drain field or contaminate groundwater and nearby wells.
Generally speaking, state health agencies do not recommend septic system additives. If a system is properly designed, and not abused by dumping garbage or chemicals down toilets, the only maintenance needed is inspection and tank pumping.

March 2003 POPULAR MECHANICS.com

Of course if you believe there are 500 mile per gallon carbs repressed by the evil oil companies, that Elvis is alive and well, or that the Government has several frozen corpses of "greys" then I'm sure you will see right through my flimsy attempt to spread malicious lies about the fine upstanding marketers of septic aditives.