As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER DEPARTURE WE RECEIVED SMOKE TOILET CAUTION MESSAGE. WITH A SLIGHT HAZE AND A MUSTY SMELL IN THE CABIN. WE RETURNED TO THE FIELD. SMOKE TOILET CAUTION MESSAGE WENT AWAY, BEFORE WE LANDED. (FLT#5074) FO: 02/18/2019 CLOSED REMOVED AND REPLACED LH ENGINE PRESSURE REGULATING VALVE ASSY IAW AMM.