I've read many reports on the darkroom newsgroup and the general consensus is it's okay, just don't dump bleaches or unrecovered fix down the septic system as the silver has an adverse effect on biosystems. Everything else is pretty benign. Also be wary of selenium or other heavy metals going down the drain.
You can either desilver the chemicals with steel wool or save it and take it to a proper recovery outfit, a chat with local photofinisher might give you a good lead as to where to take it.
Washing film and prints has such a low silver washout that it's no worry for the septic system.
Also try to neutralise large quantities of alkalies or acids by combining them before disposal.