According to Wisconsin Plumbing Code, nearly anything fixture that handles cleaning agents must be drained to the sanitary drain (the septic tank/system). This includes sinks, showers, washing machines, dishwashers, etc.
This that may be able to be drained to grade (not in the septic system): Condensate from furnace, air conditioner, drainage sump pump discharge, dehumidifier condensate and an outside shower used only for rinsing, not washing
Please consult the Wisconsin Plumbing Code