Those who work with Docker know how fast is free space disappearing, especially, in case you are experimenting with some new features and don’t pay much attention to cleaning up. As the result, a lot of empty untagged containers can eat tens of gigabytes of space.
Here is the one-liner I found to be very useful for removing old stuff:
docker ps -a | grep 'weeks ago' | awk '{print $1}' | xargs --no-run-if-empty docker rm
Actually, I’m not the one who came up with this answer, but I spent a few hours trying different commands and googling for the answer.
Here is the full Docker cheat sheet that I bumped into and found it being quite good itself:
Cloud Application Security 