WordPress features a trash bin, which was add in version 2.9. The trash bin contains any content that you have deleted and automatically empties every 30 days.You can change the 30 days to another interval, by adding the following to your wp-config.php file.
define( 'EMPTY_TRASH_DAYS', 7 );
You trash bin will be automatically emptied every 7 days. Change the 7 to whatever you want.
By changing the 7 to a 0, the trash bin will be disabled and will be replaced with a delete permanently link.