Just to play devil's advocate... it's wash water for a reason and the reason is that it is still washing chemicals out of the paper. At what point they become "trace" I'm not sure. I also worry about this since we are on a septic system at my house. So far, I use RC paper, processed one at a time and the first rinse is for > 1 minute and vigorous and goes into jugs for disposal. After that I rinse them in the sink and let it go into the septic. This topic has come up before and I still plan to do some testing for residual silver to attempt to make these sorts of processing decisions based on some real evidence rather than "what someone on the internet says"....

I have a large vegetable garden and I don't think I'd let photo chems go into that at any concentration.