Google septic pumping chart:

http://www.nowra.org/files/KnowYourS...g% 20chart%22

1. Household chemicals like bleach don't hurt the septic system.
Microbes are everywhere and re-establish themselves automatically and
quickly. Even if you amazingly manage to sterilize the tank water,
microbes are in your waste and in your tank and pipe walls.

2. Additives are a scam.

3. Garbage disposals are practically standard equipment for a modern
kitchen and are very convenient. There's no need no deprive yourself
of one. Just check the septic pumping charts and adust your pumping
schedule accordingly. Pumping out a septic tank is CHEAP.