If you want that system automatically purges the content from cPanel user's File manager trash:
- login to WHM
- go to Tweak Settings
- select "Age, in days, of content to purge from users’ File Manager Trash "
- set the desider number of days (i.e., 30)
- click on "Save"
If you select "Disabled" (which is the default), trash contents will be saved indefinitely.