I was amused to note that only 2 multiples of digits only have 1 sink (3:-> 495 and 4->6174)
But for all the others that have a sink, One of the solutions will contain 6, 1, 7, and 4 while the other will contain 4, 9, and 5
10 has 3 sinks. 2 of them contain 6, 1, 7, 4 and 2 of them contain 4, 9, and 5 (One sink contains both sets)