Set your slow cooker in the freezer for two to three hours. Remove the slow cooker and scrape burnt-on food residue off with a rubber spatula. Wipe the removed stains out of the slow cooker with a damp paper towel.
Pour a quarter-sized amount of liquid fabric softener on a clean cloth. Rub the fabric softener into the remaining burned-on food stains. Let the fabric softener soak into the remaining stains for three minutes to soften them.
Fill your slow cooker with enough water to cover any remaining burnt food stains. Add five to 10 drops of dishwashing detergent. Place the lid on the slow cooker.
Plug in the slow cooker and turn it on the "Low" setting. Heat the detergent solution in the slow cooker for one hour. Turn off the slow cooker and unplug it. Allow the solution to cool until it's warm.
Empty the slow cooker of the detergent solution, except for an inch in the bottom. Ensure the electrical cord and outside of the slow cooker don't get wet while you empty the solution. Wipe the outside of the slow cooker with paper towels to remove moisture.
Scrub the inside of the slow cooker with a nylon mesh scrubber to remove the last traces of burnt-on food. Rinse the inside with warm water until the detergent solution is gone.
Dry your slow cooker thoroughly with a lint-free kitchen towel.