This article explains how to delete all items in the Deleted Items folder and the Junk Email folder on Outlook.com.
How to Empty the Deleted Items Folder in Outlook.com
When you delete messages in your Outlook.com account, Outlook moves those messages to the Deleted Items folder. Before you clear your account of clutter and deleted items, go through them to make sure you haven't missed anything important.
To empty the Junk Email and Deleted Items folders:
In the Folders pane, right-click the Deleted Items folder.