- Log into webmail
- Click "Mail" in the menu at the top of the page, this will show you your inbox
- In the column on the left side of the screen, click the "Trash" folder to view the items in the folder
- In the column on the left side of the screen, right click on the "Trash" folder, then click "Empty"
Clicking "Empty" will empty the folder on the server.
Warning: Clicking "Delete" will delete the whole folder, rather than just clearing the items in the folder.