What was found
CLT FLT 721 EN ROUTE FCO TO CLT. STRONG SMELL OF URINE IN VICINITY OF AND FORWARD OF AFT LEFT LAV BY 4L DOOR. MAINTENANCE FOUND BOTH WASTE TANK WASTE SEPARATOR FILTERS VERY DIRTY AND VERY STRONG URINE SMELL COMING FROM BOTH SEPARATORS. ALSO O-RING WAS MISPLACED FOR AFT TANK WASTE SEPARATOR. CLEANED BOTH WASTE SEPARATOR HOUSINGS AND REPLACED FILTERS AND O-RINGS FOR BOTH WASTE SEPARATORS. OP'S CHECK TOILET SYSTEM. ON LEAKS OR ODOR OBSERVED FROM INSIDE CABIN OR IN LOWER COMPARTMENT IN AFT BAGGAGE.