Problem
We used Arch Linux for a while, updating regularly using Pacman. We used Docker for Development and/or other reasons. Now there are hidden files on our Machine, that claim a lot of Space.
Solution
Clean Pacman
Delete old PacMan Packages from Cache by running this in Terminal:
sudo paccache -r
Clean Docker
Delete all Docker Images. But do now worry. You can always rebuild them or pull them from DockerHub.
sudo docker system prune -a -f