Apply a teaspoon of cornstarch to the stained area and allow it to set overnight. The cornstarch works by drawing the grease out of the material. The next morning, rub some grease-cutting dish detergent into the stain and allow it to set for approximately 10 minutes before washing it in a washing machine. The dish detergent will break up any grease that was left after the corn starch application.
Use an old toothbrush to rub shampoo into the entire area affected with grease. The shampoo is effective at cutting through oils on fabrics the same way it works on hair. Allow the shampoo to set for approximately 15 minutes before washing the pants in the washing machine.
Spray a small amount of WD-40 on the area affected with grease and gently scrub it into the material using an old toothbrush or a soft cloth or sponge. Allow it to set for approximately five minutes, then scrub the area again. Apply grease-cutting dish detergent to the area and rub it in to break up the WD-40 and the grease. Wash the pants in the washing machine as usual.
Rinse the area of the pants affected with grease under hot water in the sink. Situate the stain directly under the faucet and let the hot water pour directly on it until the stain can no longer be seen, then wash the pants in the washing machine as usual.