What was found
AT 23:10 (APROX) AFT F/A SMELLED "DIRTY SOCK" SMELL AT ABOUT 1,500FT ON TAKEOFF. BLEEDS WERE IN NORMAL T/O POSITION (ENG 1+2 BLEED ON, AFT BLEED OFF L. PACK AUTO, ISOL AUTO, R PACK AUTO). SEEMED TO BE IN THE AFT LEFT GALLEY IT WAS A LEVEL 3 AIR QUALITY EVENT. THE SMELL AGAIN GOT STRONGER ON LANDING. IT WAS PERSISTENT THROUGHOUT THE FLIGHT. CHEMICAL SMELL AT 10,000 FT ALSO. GROUNDED - YES. TROUBLESHOT REFERENCED B737-9 IFIM TASK 21-00-00-810-830 FOUND SMELL TO BE COMING FROM AFT GALLEY DRAIN CLEANED GRAY WATER SYSTEM IAW B737-9 AMM 38-31-00. NO ODOR REMAINS.