Set WordPress to Automatically Empty the Trash
I found this simple, handy tip over at wprecipes.com. You can set the automatic interval at which WordPress must empty the trash by adding this to your wp-config.php file:
define('EMPTY_TRASH_DAYS', 10 );
The number 10 refers to how many days between WordPress trash dumps. Set a “Garbage Day” interval that is convenient for you and start saving a little space.