I used "Social Book Manager" in the chrome store to (painfully, repeatedly) flush out all content from my account down to the last Like. Walk away and your account appears 100% empty until a reactivated friend occurs, then all your stuff linked to their content magically reappears for you to try and delete again. So I sat on it for another year, periodically logging back in to flush out whatever hidden content had reappeared.
Having now (this Jan.) deleted my supposedly "empty" 10yr old account, it's good to know the hidden content is being removed properly, as my intent was to 100% scrub myself from their service and boy did I try.