As one additional comment..the small amounts you discard from home processing will in no way effect your municipal waste disposal system, or in general, will not harm your septic system (if that is what you use). It is only when you get into the very large disposal issues of a large-volume laboratory that you have to be concerned. We're talking about hundreds of gallons a week. This subject of chemistry disposal for amateur processing was well and comprehensively covered in back issues of Darkroom Techniques by their resident photochemical engineer, and the general consensus was that there is no need for concern in the small quantites used for home processing.