In general, don’t pour anything into a storm drain. It will end up in your local lakes and rivers. This includes anything left out in the street or parking lots.
The sewage system in most cities and municipalities is a closed system, which is run by licensed water operators. It is their job to neutralize their effluents, and ground any metals or toxins which they contain. There are things which water operators like: neutral solutions, base solutions (drain cleaners), colonizing bacteria and their food stuffs. There are things they don’t like: acids, pharmaceuticals (antibiotics go a long way in killing off friendly bacteria), bright metals (Silver was one of the 1st antibiotics), pesticides, petroleum products. None of these should go into the sewer system.