Ok, first let me say that household hazardous waste is exempt from EPA rules. The thinking behind this is that it would be generated in such small quantities as to be almost if not totally negligible. So although LFguy is correct in his assesment the quantity of silver found in your fixer after dilution would not cause any problem. Unless you have a home business where you are continually processing you have nothing to worry about. The only thing which could be of concern is if you have copper piping, if you do, then flushing with some water after you dump the chemicals would be good.