A person who is really into most if not all types of
anal/ass play (see muck dugout). Not to be confused with "muck chucking" although the terms can be used interchangeably.
Muck refers to mostly feces in this
case but it surely is not limited to it (see muck chucking).
Person A: "Oh
boy, he's waist deep in that tar pit, we should probably
help and get him out before it's too late."
Person B: "You're right, you could say he is halfway to becoming a real
Muck Daddy"