I believe they are mostly not even ashes, just ground up bone fragments

Last time they came around I decided to give it a shot. Best way was just pan fried with butter. Crunchy, slightly nutty flavor. Not bad at all and lots of free food.

If you want to clear out any stopped containers, orphaned images, networks, etc run “docker system prune”

What I think is happening is there is a persistent volume mount that needs to be cleared out. If you’re using the docker run command with a -v flag, check the host path. It’s likely there are saved configurations you’re passing into the container.