The environmental laws really kick in when you decide to do photography as a business rather than a hobby. The environmental laws are all about $$$ - which is why most household chemicals are exempted and it's only when you operate a business that the rules kick in.
I'm going through this now, as I have given thought to commercializing my photography. The local water company requires full testing of the waste stream, which costs $800, at least once a year. And they will only permit silver levels of 0.005mg/L which is 1,000 times lower than the EPA designation of hazardous. I think they have made a mistake, but they insist not. Interim testing for certain parameters is also required. Although much of photographic waste is not hazardous, the testing is expensive and at the end of the day, there is no practical way to bring silver down to 0.005mg/L, so I will have to find another way to dispose of it (maybe use silver reduction and then mix it with A LOT of developer). EPA rules also forbid dilution as a method of rendering a hazardous substance non-hazardous, so I'd have to have my fixer below 5mg/L before I could mix it with something else.
You end up having to be a lawyer to comply, and I find that the local environmental folks often don't understand the rules themselves. And because the rules focus mainly on concentrations rather than volumes, it is much harder cost-wise for very small businesses to comply than large ones.
Finally -for very small users, Google "Chemgon" Essentially a 5 gallon jug for about $50 that contains sodium polyacrylate - which will turn a pH neutralized fixer into a solid that will not leech silver, and the unit can then be thrown in the garbage. I have no affiliation with them other than to have bought a couple, and they seem to work and the local waste dept ultimately signed off on them.