I went through the same angst when I moved to this house with a septic tank. My biggest concern was silver saturated fixer, so I bought the silver recovery system that john nanian here sells. Spent fixer goes through a silver magnet, then through the trickle tank before heading down the septic. Film is washed per the Ilford method with wash water going through the trickle tank. Print holding water and hypo clear goes through the trickle tank as well. Hopefully so little silver is left when the prints go in the washer to not matter.
Just to be on the safe side, and because I like to be "green," I switched to LPD paper developer that I replenish and reuse, reducing those chemicals into the waste stream. My film developer is very dilute, and people tell me there is more of the same kinds of chemicals in the food I eat.