What was found
AFTER TAKEOFF, REACHING ACCELERATION ALTITUDE RECEIVED A LAVATORY SMOKE INDICATION ON THE EICAS. RAN LAVATORY SMOKE CHECKLIST, FLIGHT ATTENDANT INVESTIGATED LAVATORY. NO SMOKE WAS FOUND. FLIGHT ATTENDANT REPORTED THAT A WHITE COLOR MIST WAS COMING FROM THE FLOOR VENTS AT ROW 8 AND IT SMELLED LIKE A WET MOLDY SOCK. CREW DECLARED AN EMERGENCY AND RETURNED FOR LANDING. AIRCRAFT LANDED WITHOUT INCIDENT. PERFORM EM-72-034R4. NO ODOR NOTED. PERFORM OPS CHECK OF LAVATORY SMOKE DETECTOR SYS IAW 26-14-00. OPS CHECKED GOOD. FOUND WATER COLLECTOR CLOGGED, UNCLOGGED DRAIN IAW 21-51-05. FOUND RECIRCULATION MUFFLER LOOSE, SECURED IAW 21-24-02. AIRCRAFT RETURNED TO SERVICE.