why wouldnt it be good flushing copper sulfate down the drain?
Because it is toxic to many organisms?
Copper sulfate is used as a disease control mechanism for crops. It is highly soluble in water and its effects on aquatic organisms are concerning. By concerning I mean it has a pretty low probable effect level (PEL) and LD50 (lethal dose for 50% of the population). So dumping it down the drain would quickly allow it into aquatic ecosystems since sewage treatment plants have no way of removing it from the water. Cheers, Andrew