Oh, when ice does fall from an airliner, it usually originates from the sinks and water dispensers, NOT from the toilet. The public immediately assumes it is toilet waste water..
I can't figure out how it could be from sinks and water dispensers. Drain masts are heated. If they are not heated (due to a malfunction), the pipes are relatively narrow (<1/2"?) and water usually doesn't get through.... it freezes, causing blockages and floods. Also, wouldn't the narrow shape of the mast out in the airstream not let large chunks accumulate?