When Joomla 1.7 Articles are Trashed they are still in the database.
To empty the Joomla 1.7 Trash go to:
Content -> Article Manager
In the "Select Status" drop down menu select "Trashed".
Select the articles to remove from Trash and click the "Empty Trash" icon in top right toolbar.
If you have many articles to delete you may find it faster to run this SQL in PhpMyAdmin:
DELETE FROM `jos_content` WHERE `state` = "-2"
(the jos_ table prefix may need to be replaced with your custom prefix)
