campden fruit question

working on a blackberry wit. i have checked the site and can't find a concensus on how to use the campden tabs. from what i gather, i clean the blackberrys, puree and then add campden tabs to sanitize. how do i add the campden tabs if i am using 5lbs of blackberrys? do i add a tab/multiple tabs to the puree and then add to secondary? do i add the puree to the secondary and then add tab/s? do i puree, add water (in order to help dissolve) and then add to secondary? how many tabs should i use? any help would be greatly appreciated. thanks