For the small volume I've been doing where I have a septic tank, I empty depleted developer, the used fixer, and a first tank of wash water into a plastic jug. I have another place where I can discard it where it will be treated in a municipal treatment plant.

Based on the research I did on APUG and other sites, I'm not concerned with putting a few rolls worth of developer a week into my septic tank, but would not put the used silver down the drain.