Fill the bathtub about three quarters full with hot water and add the dye to the water according to the directions on the bottle. (See the link in Resources for information on various types of dyes.) If you are mixing colors, add the second dye. Some dyes, such as RIT dyes, give the best end result when you use boiling water. If this is the case, boil water on your stove in several pots and then carefully add it to the bathtub until the desired amount of water is retained.
Run the spatula along the bottom of the bathtub to help stir the dye in so there will be no streaks in your rug's coloring. Stir the water gently for about 30 seconds.
Place the rug down into the water, completely submerging the entire rug. Use the spatula to push the edges down into the dyed water, so that you do not get dye on your hands.
Allow the rug to sit in the tub until the desired color is achieved. If you mixed colored dyes, make sure that you have no spots on the rug in the water that only hold one color. Continuously stir the water while the rug is immersed to keep the dyes from settling out.
Remove the rug from the water and drain and rinse the tub. Rinse the rug out in cold water and then hang on the drying rack. If you don't have a drying rack, lay towels out on the floor and straighten the rug out over the towels and allow it to air dry in this manner.