(defadvice planner-create-task-from-buffer (before paul activate)
  "Automatically schedule task onto TaskPool as well as other projects."
  (if plan-page
      (unless (string-match plan-page "TaskPool")
        (setq plan-page (concat plan-page planner-multi-separator "TaskPool")))
    (setq plan-page "TaskPool")))

Here’s another snippet that will unschedule tasks from TaskPool when
you mark them completed with C-c C-x (planner-task-done). Nifty stuff,
huh?

(defadvice planner-task-done (after paul activate)
  "Remove completed tasks from the TaskPool if that still leaves them linked."
  (let ((info (planner-current-task-info)))
    (when (planner-task-link-text info)
      ;; If it is linked to TaskPool _and_ at least one other thing
      (if (string-match planner-multi-separator (planner-task-link-text info))
          (planner-multi-replan-task
           (planner-multi-make-link (planner-multi-filter-links "^TaskPool$" (planner-multi-task-link-as-list info) t)))
        ;; Else if it has a date and is linked to TaskPool
        (if (and (planner-task-date info)
                 (string= (planner-task-link info) "TaskPool"))
            (planner-replan-task nil))))))