"Faux Floo" was a term used by employees of St Mungo's Hospital for Magical Maladies and Injuries to describe various kinds of homemade powder that witches and wizards tried unsuccessfully to use as a substitute for Floo Powder. One variety that was used apparently consisted of powdered Runespoor fangs.
The use of such powders was dangerous, and could result in burns, or people getting blown out of their chimneys. Healers at St Mungo's had to treat a patient suffering from a "Faux Floo" injury at least once a year.
In 2010, Rutherford Poke, Healer and St Mungo's spokeswizard, lamented "Faux Floo" injuries, reminding people that genuine Floo Powder only cost two Sickles a scoop, and swearing that he would not treat the next wizard who came into St Mungo's with a burned bottom.
- Pottermore (Mentioned only)