OK, didn't find the original sources, but this is from Clorox (obviously biased, but I doubt their lawyers would let them get away with lying on this):
Q. I use bleach in my white wash, but also have a septic tank. I need to be careful about how much bleach I use, so as not to kill the bacteria in the tank. We are a family of four adults, but have occasional invasions of germy little grandchildren. Any ideas?
A. I can put your mind at ease regarding using Clorox® Regular-Bleach and your fear of harming your septic tank bacteria. As long as you use the recommended amount (3/4 cup per wash), the bulk of the sodium hypochlorite active will be broken down to salt and water while attacking the stains, soils and germs in the wash load. Any un-reacted hypochlorite will find lots of "things" to react with going down the pipes before it enters your septic tank field to be converted into salt and water. So as long as you’re not pouring a whole bottle down the drain, you have nothing to fear and those germy grandkids can have the cleanest, whitest clothes while visiting.
- See more at:
Septic Tanks and Bleach
And that makes sense to me that much of the bleach would be broken down in the wash cycle. The key to sanitizing is 'clean, then sanitize' - dirt/gunk breaks down a chemical sanitizer.
22 yrs for us (2 of us), and the house is 5 yrs older. Never any problem. Plumber friend says disturbing the system if not needed can ruin it, and Industrial Hygienist friend says feces is 50% bacteria by weight, ...
Knocking on wood here.
Instead of knocking on wood, get your tank pumped!
That 50% bacteria is part of the solution and part of the problem. Yes, it means you don't need to add bacteria to the tank, but those bacteria eventually die and some components of them settle out to the bottom of the tank and start to fill it up. That reduces the capacity, and more and more unprocessed stuff enters the drain field. That's bad, and drain fields are expensive to replace (the $20,000 mentioned earlier would be a ballpark). Newer regs might have tighter restrictions than when first installed, so you might be facing a very expensive replacement, could be that size system would not be allowed, and you'll have to go more 'high tech' ($$$).
Seriously, read up on some .gov and .edu sites for some
real info rather than some random anecdotes about people who did this or that and 'never had a problem' (have they dug up and inspected their drain field to see how well it is functioning?). You likely won't be aware of a problem until it is too late (and very expensive).
edit/add: and
another thing.... If you have not had your tank pumped, have you had it inspected? Tanks have a 'baffle' at the outlet - the baffle pulls the water from just below the surface, so that grease and other scum don't enter the drain field (grease is bad for the drain field). Those baffles often fall apart after a while, and need to be replaced. When they pump the tank, they inspect the baffle. So if your baffle has been non-functional for the past ten years or so (very likely), your drain field has really been compromised.
When you sell your house, the county or any other inspection service is sure to have an issue with a tank that hasn't been maintained in decades. It's gonna cost you!
-ERD50
at all during the rest of my entire life. I may not long for international travel, but I think that living in a location with city water/sewage is a great way to spend my discretionary money. YMMV
And at my house it just disappears when I flush and I don't have to deal with it, or even think about it. 
