Robharr's dashboard

Is there any way to purge completed tasks in all projects without having to do each item individually? When I check a task as done, it removes it from my today view, but the item is still listed under my project (Checked and grayed out). This is fine, but after a period of time I want to be able to purge all of my completed tasks.

Is there a way to edit tasks directly in "Today" once they've been created?