How do I remove a black residue after seasoning cast iron waffle maker
You might consider removing all that seasoning with oven cleaner and starting over to get a thin, even coating. Thick, gummy seasoning is not going to perform properly.

These are the best instructions for cast iron seasoning I know, using multiple very thin layers of flax seed oil:
http://www.youtube.com/watch?v=xoIO8YOpyN4