What was found
UPON PREFLIGHT OF THE AIRCRAFT, AND AFTER SITTING OUTSIDE OF THE HANGAR DURING A RAINSTORM, 2 OR 3 SUMP GLASSES WERE FILLED WITH WATER FROM EACH WING FUEL TANK SUMP DRAIN. FURTHER INSPECTION OF 9 OTHER AC OF THE SAME MAKE AND MODEL FOUND 2 OTHER AC WITH SIMILAR AMOUNTS OF WATER IN THE SUMP DRAINS. ALL 3 OF THESE AC WERE TIED DOWN OUTSIDE DURING WEATHER ABOVE STATED. INSPECTION OF THE FUEL FILLER FLANGE/CAP ASSY ON ALL 12 AIRCRAFT REVEALED THE SAME LOOSE FUEL CAP CONDITION. ALL AC FUEL CAPS WERE TIGHTENED AS A PRECAUTION. THE O-RING SEALS DID NOT APPEAR TO BE DAMAGED. (K)