Planes dumping toilet ice?
What happens is a seal leaks on the exterior connection of the aircraft where the sewage is pumped out. As the plane flies at cruise altitude, around 25-35k feet, the temperature is -80°F and the liquid freezes almost instantly and sticks to the skin of the plane.
As the plane descends to land, the temperature rises and the nasty ice falls off, usually in a remote wooded area, never seen by anybody but bears and deer................