What are Trash and .Trash-1000?
GNOMEish file managers need a place to put trashed files.
- Deleted files on your "home" partition go to:
/home/username/.local/share/Trash - Deleted files on other partitions can't be copied there for performance and space reasons.
So it tries to put them in the /.Trash-$UID folder of the file's partition. Without rw access to that folder, no trash.
Run this bash in the partition root as the user who needs a trash.
sudo mkdir .Trash-$UID && sudo chown $USER:$USER .Trash-$UID
You can delete this folder and disable write access to the / to disable that feature.