As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON TAXI OUT, RECEIVED SMOKE LAV MESSAGE AND DARK SMOKE HAZE IN CABIN. AFT RECIRC FAN FILTER WAS CLOGGED. REMOVED AND REPLACED FILTER (21-21-01) AND PERFORMED FUNCTIONAL CHECK OF RECIRC FAN AND ECU. NO SMOKE NOTED. OPS CHECK GOOD (21-51-00).