Deleting Tasks

Can someone please post how to remove deleted tasks...completely. When I mark a task complete it just strikes a line thru it. Fine.There has to be a way not to combine the active tasks with the completed ones. When I select to view a task and it refreshes the page it sends me to the bottom of my tasks to the very last completed/deleted task with lines thru them. There are over 400 of them that I have to scroll back up the page to get to the task I first selected on the previous page.
Thank you.