As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PDX INFLIGHT - CREW REPORTED SMOKE IN CABIN AND COCKPIT FROM UNKNOWN SOURCE. SMOKE BEGAN TO DISSIPATE BUT SMELL AND VISIBLE SMOKE STILL PRESENT AFTER LANDING. RETURNED TO PDX AND LANDED WITHOUT INCIDENT. FOUND SMALL AMOUNT OF GLYCOL AT APU INLET. CLEANED APU INLET. SYSTEM GROUND CHECKED NORMAL OPERATION.