I spent ten years flying islanders, a fair percentage of which was in tip tank equipped fishery protection models. The transfer pump switches were identical to the boost pump switches including the direction of movement. The only difference being that they were located between the tip and main fuel gauges and had a light to say they were turned on.
What I could never fully understand was the logic of the POH checklist, for fuel transfer it said to wait until the mains were low (IIRC maybe under 15 USG). Our SOP was to start transfering about an hour into the flight (always max fuel on takeoff) so that we could visually see the tip tank contents coming down and the mains going up, the only true way of telling if the transfer pumps worked. It would afterall be a bit daft to follow the book to letter and not start transferring until the mains have an hours worth left in them with land being an hour away! I certainly aborted a flight more than once due to the pumps not performing properly.