Pour 1 gallon of water and 1 cup of white vinegar into a large pot. Heat on the stove until it reaches a boil.
Remove the pot from the heat. Submerge the dingy white garment in the hot vinegar solution using tongs. Let the garment soak overnight.
Launder the white garment in your clothes washer with 1 cup of white vinegar and 2 oz. of laundry detergent. Use cool water and the washing instructions recommended on the garment's care tag.
Hang the white garment outdoors to dry in the sun. Natural sunlight also naturally whitens whites.