Hi Olu,
One option you have is to delete the entries as soon as they are used. In your case that's probably not helpful, as you may want to use them for more than 1 browse view.
On the other hand there is no guarenteed way of knowing the user has finished with the browse. They may just close their browser, or type something into the address bar - in the web there's no guarenteed "close'.
So the best place is in the DeleteSession method (webServer). When a session is automatically deleted then this related session information can be deleted as well.
Of course you can add the code to a button or something as well if you want the user to be able to "clear the tagging" anytime they like.
Cheers
Bruce