Quote Originally Posted by Maris View Post
Even Kodak publication J-300 which is the de facto last word on "fixer down the drain" is more about avoiding potential disputes and less about the niceties of chemistry.
That's my take as well, based on personal experience. I simply posted the link for reference.

I have had a small, but nicely equipped, home darkroom in the same location now for 24 years. It's on a septic system originally installed in 1978. Using standard black-and-white processing chemicals that all eventually go down the drain, I have never had a single issue in almost a quarter-century of light hobbyist-level usage.

I do suppose YMMV, but mine never has.