I cannot believe they won't take it at your hazmat roundup! Stuff like this is exactly what the roundups are for!!!
If they are going to be putzes about it, go down to their office and dump your effluents on their lawn and/or flowers.
In all seriousness, I would chuck everything down the drain (well diluted) but used fixer and toners. I would get a silver magnet or trickle thingy from JNanian (a fellow who posts here on APUG), and then dump the fixer after treating. Until you get this thing figgered out, I would go the evaporation route with toners. Get a bug cage or fish tank with a screen top that will keep critters out, and let it sit outside on dry days. No need to remove and trash the remaining crust and toss it. That pretty much defeats the point anyhow. When you convince them to come to their senses, you can mix the crust back in with water and dispose of it that way.