I had read once that exhausted developer actually makes for a pretty good hypo clearing agent. I believe it was in The Amateur Photographer's Handbook by Aaron Sussman. Although I personally believe that an acetic acid stopbath is the best thing for halting development like a Ford Pinto slamming into a bridge abutment. Sometimes it's all you've got to salvage the print that seems to come up with runaway development. As far as contamination, if you're using a rotary washer like the old Richards, the contamination would be like peeing in the ocean.