Turn the overalls inside out and then lay them on a flat, dry surface such as a counter or the top of your washing machine, with the dirtied area exposed.
Apply enough laundry stain pre-treatment to saturate any affected areas. Rub the fabric over itself for 30 seconds to help the pre-treatment penetrate the fabric.
Allow the overalls to sit where they lay for five minutes.
Wash the overalls as usual in a washing machine, using the hot water setting and the amount of laundry detergent as directed on the specific container. Unless the overalls are heavily soiled, they can be washed along with your regular laundry.
Dry the overalls in a dryer on regular heat for 40 minutes, or by hanging them up to air dry.