A KDE Solid Action to clear the trash of a removable device such as USB memory stick or flash drive before unmounting.
This file goes into:
$HOME/.local/share/solid/actions/
Just select "Empty Device Trash" from the list of actions available for a mounted removable device.
This will remove all files from hidden directories:
<media>/.Trash-$UID/files/
<media>/.Trash-$UID/info/
For many users this is:
<media>/.Trash-1000/files/
<media>/.Trash-1000/info/