To mark a task as completed in Remember the Milk:
- Click the center of the task or (if selecting multiple tasks).
- Press C or click (top menu).
Clean Up Your Lists
If you mark tasks as completed instead of deleting them, periodically archive or delete old tasks to keep your lists trim.
To delete a task instead, press Del (Fn+Delete on a Mac).
If you mark a task as completed, Remember the Milk will archive them for you “forever” (according to their site).