I feel the insights from Rich makes much sense. Elisabeth thanks for sharing the thread "pit additives". It's extremely relevant and I even felt that I have just reframed an old question.

If at all we like to improve the septic tank's biological degradation performance, practically in any possible way, 
I think we must acknowledge and should focus on the design inadequacies in septic tanks as Rich mentioned "I have operated both aerobic and anaerobic digesters and the reality is most know a careful balance of time, mixing, temperature is required for successful operation.
I suspect septic tanks many missing elements indigestion make it at best a poor substitute with no control over mixing or temperature".

It is a never ending question, even wastewater utilities in USA are approached to buy these inoculums to treat say FOG in Pump Stations and as others have suggested my response to them is if biological why would I ever need to buy more than once.  I think most of us know how sophisticated digestion is, whether aerobic or anaerobic or septic. I have operated both aerobic and anaerobic digesters and the reality is most know a careful balance of time, mixing, temperature is required for successful operation.

I suspect septic tanks many missing elements in digestion make it at best a poor substitute with no control over mixing or temperature. The hope is sufficient digestion occurs and few compounds introduced that might thwart biological activity. I am a skeptic. I think generally speaking septic tanks and drainage fields were a cheap attempt at wastewater treatment in an era before conventional activated sludge put into practice and where collection system expense was too expensive or difficult. So what is answer, I doubt it is effective.

My suspicion from years of observation of somewhat static tanks is a layer of FOG almost as a rule forms at surface, this I would think would make any additive less likely to get through to liquid and digestion below in settled biomass. In fact it is my suspicion that FOG is typically why many septic tank systems fail and require regular pumping out.. 

Dear Vasanth,
You're right to be skeptical, and I agree with Pawan's statement of "Such advertisement is mostly commercial gimmick.".

As these ads are so pervasive, we put together the relevant information a while ago and put it into this Wikipedia article about pit additives (could be in need of updating):
en.wikipedia.org/wiki/Pit_additive

You can find several discussion threads on this topic by searching for "pit additives" here on the forum. For example this one:
forum.susana.org/280-faecal-sludge-treat...l-sludge-includes-em

There is also this sub-category on odour issues:  forum.susana.org/233-odour-issues

Feel free to continue any of those older threads (or this one) if you feel that new questions have arisen.

And yes, mixing is more important than additives.

Regards,
Elisabeth

Dear Vasanth
  Efficiency of  anaerobic cultures in markets was discussed in this Forum earlier also. 
Since human waste contains high population density of active hydrolytic bacteria, therefore, there is least or no effects of external bacteria on biodegradation of such wastes in septic tank.  There are companies who claim to have developed inoculums of bacteria to degrade wastes   effectively. Such inoculums may be suitable for kitchen wastes/ solid wastes - not for septic tank. I got tested some cultures of well known company with the control of human wastes and cold not find more effective than the control. 
As you mentioned,  inoculums needs to put at the top of the septic tank before it is filled. If it is so effective, then one should put inoculum   in septic tank on the day it is put in use. In such case, the tank will never be filled and therefore, its size can be reduced considerably.  Such advertisement is mostly commercial gimmick. 
It is common point that biodegradation continues till the substrate is stabilised. There is always residual matters. Empty of septic tank is always required. It may be longer in case of effective cultures of micro-organisms . 
Best regards

Pawan 

One thing, we can observe throughout e-commerce stores across the world is the so-called "anaerobic bacteria inoculum" for your septic tanks. The popular claims are that don't desuldge your septic tank ever, just top it up with our inoculum, every 4-6 months... goes the advertisement.

But it's so hard to find any concrete evidence for the claims and I feel it remains understudied.
I don't find any peer-reviewed journal article evaluating these inoculums and their claims (kindly let me know if you find one I would be thankful).

On the other hand, if we observe any typical anaerobic bio-digester design, the mixing mechanism is a critical component.
It can be a simple mechanical mixer or it can be that the influent feed is fed through the bottom (as in UASB) to allow gaseous mixing of the substrate and the biomass.

So this raises the question, even if the inoculum is effective (as claimed by their manufacturers), just by dropping the inoculum into a conventional septic tank can we make it work? Will the mixing be good enough? (note: the inoculum is being advertised for septic tanks that aren't desludged for years) Don't we need any mixing mechanism?

Best regards,
Vasanth.