What was found
UPON GEAR RETRACTION, NOSE GEAR STARTED RETRACTING, WE HEARD AN UNUSUAL NOISE. NLG EXTENDED BACK DOWN. A FEW SECONDS LATER RECEIVED ECAM FOR LANDING GEAR, FOLLOWED BY LOW HYD PRESS ON GREEN SYSTEM. CONFIRMED THAT WE HAD LOST ALL FLUID IN GREEN SYSTEM. WE PERFORMED ALL QRH PROC AND DID A MANUAL GEAR EXTENSION. REPLACED GREEN SYSTEM CASE DRAIN FILTER. NO PARTICLES FOUND. RETORQUED LINES ON CASE DRAIN FILTER ASSY PER AMM 20-21-12 LEAK CHECK REQUIREDC/W GREEN SYSTEM BLEEDING PER AMM 29-00-00-870-002-A & 29-00-00-870-003-A.