How to do it:
Soften the stain to prepare it for removal. For a dry mustard stain, soak the fabric in cool water mixed with color-safe oxygenated bleach for up to an hour. You may have to soak several times for best results.
If the stain is fresh, go directly to the next step.
Scrape off excess mustard from the fabric using a dull knife or spoon. Be sure to do so gently to prevent ripping the fibers.
Turn the stained area upside down and rinse it with cold water. Get as much of the stain out as possible.
Be sure to use only cold water, as hot water will make it more difficult to remove.
Time to spot treat. You can do this by taking a liquid laundry detergent and rubbing it into the stain. Allow it to rest for up to 10 minutes and then rinse thoroughly.
You can also use dish detergent if laundry detergent is unavailable.
Wash your mustardy piece of clothing using a stain remover. Apply the laundry stain remover to the stain and wash per the instructions on the clothing label.
Check the stained area before drying and repeat the steps above if the stain is still not removed. Once you are satisfied the stain is gone, then you can dry the clothes.