I painted this unit a while ago and was the first time I put my experimenting with slime drips to use on a finished unit.
I found it a surprisingly simple technique for the results.
First, get some cotton wool and pull apart a small pinch of strands:
Pull and roll between your fingers the strands to make a fibre:
Super glue one end of the strand to the model, and if the non glued end is fraying, I just used plastic cutters to remove a few millimetres.
Next i just got a large brush, loaded it heavily with Nurgles Rot, and then dabbed it against the cotton wool strand to finish the look: