The primary constituent of standard developers is—what?—sodium sulfite? That stuff used in massive quantities to preserve the food that you eat? And the developing agents themselves are so notorious for self-oxidizing and loosing strength that there are gazillions of APUG threads about how to slow that process down long enough that we can reasonably use them before they quickly go bad.
Standard stop bath? That stuff that's really just half-strength white vinegar? Vinegar itself being a well-known emergency substitute in the darkroom? And also being a well-known one-half of a tasty salad dressing? Except that at half-strength it wouldn't even make such a good dressing, would it? It wouldn't even be strong enough to want to eat it.
Fixer? Standard sodium thiosulfate? That stuff used by caretakers of municipal public swimming pools to dechlorinate the water when required? That same water the public swims in, pees in, and yes, sometimes even swallows? The same stuff used to pre-treat water for aquariums that arguably contain the most delicate life forms (tropical fish) in the universe? Some have even reported using sodium thiosulfate to fertilize their vegetable gardens.
And the silver ions in spent fixer? As has been pointed out, the reduction environment in which they find themselves in a septic system almost instantly results in formation of insoluable silver sulfide. Insoluable. As in not a danger to the environment. Or the septic tank.* Or even a well-toned sepia print.
Contrary to popular opinion driven by fear, a standard b&w photographic darkroom is not Bhopal, India...
* Now approaching a quarter-century using the same tank without any problem whatsoever.