What was found
SEA- WITH APU RUNNING AND BLEED AIR SWITCH OUT/OFF. WE WERE DEICING AT THE TIME AND A/C FILLED WITH SMOKE AND SMELLED LIKE DE ICE FLUID. GROUND RAN ACFT, PURGED ALL BLEEDS, GASPERS AND VENTS OF RESIDUAL DE ICE FLUID. OBSERVED FOR ANY REMAINING EVIDENCE OF DE ICE FLUID, NONE NOTED. CLEANED CABIN OF ANY DE ICE FLUID RESIDUE. PLACED APU ON MEL PER MEL 49-00-1. AIRCRAFT RETURNED TO SERVICE.