What was found
(CAN) DURING CRUISE, THE CREW STARTED TO TRANSFER TIP FUEL WITH NO PROBLEM. WHEN THE CREW SELECTED TIP TRANSFER OFF, THE RT TIP TANK CONTINUED TO FLOW UNTIL TIP TANK PRESSURE WAS EXHAUSTED. THIS CAUSED ABOUT A 15 GALLON FUEL IMBALANCE BETWEEN THE TIP TANKS (RT LIGHTER). DURING LANDING AND TAXI WITH A FULL MAIN TANK AND THE LEFT WING LOW DUE TO THE FUEL IMBALANCE, A SMALL AMOUNT OF FUEL PASSED BY THE SNORKLE CHECK VALVE AND ACCUMULATED IN THE VENT SYSTEM, WHICH DRAINED ONTO THE GROUND SLOWLY AFTER THE AIRCRAFT WAS PARKED. THE VALVE WAS REPLACED WITH A SERVICEABLE VALVE AND THE AIRCRAFT RETURNED TO SERVICE.