Septic systems work in part by the soil filtering the effluent so by the time it gets to the groundwater it is fit enough to drink. If this didn't happen, there would be contaminated groundwater everywhere. Think of all the things people pour down their drains--soaps, detergents, household cleaning chemicals, and who knows what else. So I doubt if you need to worry about any harm to the environment. To reiterate what has been said before on this site, the only problem might be silver or silver compounds interfering with bacterial action that breaks down solid wastes. But again the small amount a typical home darkroom worker uses would likely not pose a problem compared to a big lab. I have been pouring all my chemistry down the drain for years and when my tank has been pumped I have never been told of any problems, nor have I heard of any cases where it has happened.
Originally Posted by DSLR