At the amounts most home photographers use, except for silver, by the time the diluted effluent reaches the sewer treatment plant, those chemicals would be virtually undetectable unless somebody was doing some very sensitive testing and analysis, probably using a mass spectrometer. Even then, the levels would probably be barely detectable. Even at 100 times that amount, it wouldn't amount to spit in the ocean. The chemicals and machinery at any good sewer treatment facility would easily destroy most photographic chemicals in the quantities that most of us dispose of them.

Refer to Kodak Publication J-300: "Environmental Guidelines for Amateur Photographers"
http://www.kodak.com/global/en/corp/.../pdfs/j300.pdf

Specifically, Page 3 and Page 5, Table I.

This document tells exactly what to do with your photographic effluent. Basically, with a few important exceptions, it says, "Get the silver out and dump the rest down the sewer."