1.) Log into the Administration control panel
2.) In this example, the Articles Manager will be emptied, however this applies to all the other managers in Joomla.
Go to Content > Articles
3.) Click the Search Tools button
4.) Select Trashed from the Select Status drop-down menu. All the trashed items will be filtered and displayed.
5.) Click the "Check All Items" checkbox at the top of the list...
..which checks all the boxes down the page.
6.) Click the Empty Trash button
7.) Click OK to confirm you want to delete the files.
7.) The items on this page will be deleted permanently.
8.) Return to Step #5, and repeat until the trash has been completely emptied.