[Roger Cole]

Do not dispose used fixer down the drain. It will kill necessary bacteria at the sewage plant and will deposit toxic heavy metal ions in the environment. Recover the silver or dispose of at a hazardous waste facility.

Are you so sure of that in normal hobbyist quantities? It contains silver ion but the ions won't stay ions for long in nature much less a sewage plant. Metallic silver is microbicidal but in hobbyist quantities is it really any worse than washing with antibacterial soap and washing it down the drain?