What was found
AFTER DEPARTURE FROM MSP THE CREW EXPERIENCED A LAVATORY SMOKE WARNING. AT APPROX 500 FT SMOKE TOILET CAUTION MESSAGE APPEARED. DURING THE NON NORMAL CHECKLIST MESSAGE DISAPPEARED. FA SAID NO SMOKE, BUT DID DETECT DE-ICE FLUID FROM DEICING. FLIGHT RETURNED TO MSP. THE CAPTAIN DID DECLARE AN EMERGENCY TO ATC AND RETURNED TO MSP LANDING WITHOUT FURTHER INCIDENT. COMPLIED WITH EO NR C25025: INSTALLATION OF COVER ON LAV AIR VENT.