</font><font color="blue" class="small">( We make surgical instruments and we can't flush the soapy solution water we use to clean with down the drain. They are worried about the metals. We told them they are all medical grade inert stainless metals that can be put into a body. How can soapy water with trace amounts of these metals be harmful?)</font>
Well I think I can answer that one. It's probably the chromium. chromium has interesting chemistry - it is a vital nutrient when it is in its "III" oxidation state but in its "VI" oxidation state (called hexavalent chromium) it is toxic - a real bad chemical. Hexavalent chromium is pretty scarce naturally, but it is used in industrial processes such as welding stainless steel. It is soluble, so it could be in the water used to wash newly manufactured stainless steel parts.
You really, really, really, _don't_ want hexavalent chromium in the water supply.
Now the chromium in the surface of stainless steel which makes it stainless, is trivalent; it is chromium (III). This is why it's OK to put it in people, etc.
It's not at all unusual for elements in different oxidation states to have completely different properties, including different toxicities to humans. For example the treatment of leishmaniasis depends on using compounds of antimony(V) which are not so toxic to humans, but which the leishmaniasis parasite changes into antimony(III) which is deadly to the parasite. Antimony (III) is toxic to the human, too, so people no longer give antimony (III) compounds to leishmaniasis patients! So the interesting thing here is that the change in toxicity to humans due to the change in oxidation state is the key to this successful treatment.