It was common to do downspouts into sewers around here many many years ago, and some people doing it DIY still do. But it is illegal to do now, due to the number of people living in the area now, it overloads the sanitary sewer system. Many of the rural areas now have sewers and people have to disconnect from their septic tanks too. Those rural areas add to the sanitary sewer load.I didn't even know there were separate lines. Why does the sanitary line have an opening to the outside where someone can route their downspout to it anyways? (I'm imagning something that looks like a storm sewer drain but is for the sanitary line).