To begin, soak the comforter in the tub filled with warm water.
Next, pour in a small cup of baking soda, a small cup of white vinegar, and a small cup of dishwashing liquid or Marseille soap.
Leave it on overnight.
The next day, scrub the stains and then rinse the comforter thoroughly.
Wring the quilt with someone else's help. If the filling is facing down, avoid twisting the quilt too much.
All you need to do is hang it outside to dry naturally.