I would simply dispose of the photo chemicals as suggested by the manufacturer.
You have suggested this several times now, so I finally went into my darkroom (which functions now primarily as a museum to my pre-digital life) to check out the labels on the likeliest toxic chemicals I could find. I no longer have Potassium Fericyanide around, because I took that to a toxic chemicals collection sit a few years ago. But I still have the usual darkroom suspects: developers, stop bath, fixer, and selenium toner. Much to my surprise, the disposal instructions on those labels were exactly the same as on a bottle of orange juice -- namely, none at all!
Kodak Professional Selenium Toner has lots of warnings about misuse ("Harmful if absorbed through skin or swallowed," "Keep out of reach of children," "Call a physician or poison control center immediately," etc.) but not a word about disposal.
Googling on "kodak selenium toner disposal procedures" brought a bit more information, including a pdf available from Kodak
( [a href=\"http://www.kodak.com/global/en/corp/environment/kes/pubs/pdfs/j300.pdf]http://www.kodak.com/global/en/corp/enviro...s/pdfs/j300.pdf[/url]] )
which does suggest procedures for amateur photographers. A much over-simplified summary is that most
ordinary photographic chemicals are best disposed of through a municipal sewer system, in highly dilute state. The principal exception is selenium toner, which should be taken to a household hazardous waste collection site (even the empty container!). And, as one might guess, most of these chemicals should not
be put into a septic system.
I couldn't find anything in the Kodak pamphlet about burying the chemicals in a neighbor's yard and growing tomatoes on them (but, of course, that's what I do with all my spent nuclear rods. )
This pamphlet still doesn't address the question of what to do with dilute
selenium toner after you use it. For example, should you bottle all your washe water (after toning) and take it to a household hazardous waste collection site? Or maybe send half of it to you and the other half to Ray and see what happens.
I'm even a little more glad I've moved to digital. Of course, there are all those toxic computer parts to be disposed of, too, so I guess you can't win.