In a large skillet, combine beef, water, mustard, and sugar. Simmer over medium heat until the beef is cooked through, about 5 minutes. Break up clumps of meat with a spoon.
Drain the fat – but leave just a bit in there for flavor
Add the ground beef to the slow cooker
Add all remaining ingredients to the slow cooker except for the buns
Give it a mix
Cover and cook on LOW for 2-3 hours
Top with your favorites: ketchup, more mustard, mayo, sliced pickles, slice of American or Cheddar cheese…so good