Backwashing is a real pain in the arse for me. I have neighbors all around and it's too far to get to the storm sewer down the road. I pump mine into the public sanitary sewer using a large trash can as a reservoir (using gravity to drain from the trash can into the sewer.

I'm sure that's not allowed, but I don't know what else to do. I seriously doubt it's any health concern. It can easily be filtered out and there are a lot worse things that go into the sewer.