What was found
PLEASE REVISE RECORD FROM USAABB08116 TO USAABB08117. PHL FLT 723 EN-ROUTE DUB TO PHL. DURING DESCENT INTO PHL, THE LEFT HYDRAULIC SYSTEM QUANTITY DECREASED TO ZERO AND THE SYSTEM PRESSURE LIGHT ILLUMINATED. ALSO, EICAS MESSAGE "G L HYD SYS PRESS" DISPLAYED. THE FLIGHT LANDED SAFELY AND WAS ABLE TO TAXI OFF THE RUNWAY, BUT WAS TOWED TO THE GATE. MAINTENANCE REPLACED A HYDRAULIC DRAIN TUBE. SYSTEM OPERATIONALLY AND LEAK CHECKS OK.