Soak up any liquid with paper or cloth towels. Press down firmly on the towel to soak liquid from deep within the mattress. Standing on the towel may yield the best results. Repeat using dry towels until you cannot absorb any more liquid.
Pour vinegar or a commercial cleaning product generously onto the stained area. Ideally, the product should penetrate as deeply as the original liquid.
Allow the vinegar or product to penetrate the spot for at least an hour.
Press another dry towel firmly onto the mattress to absorb extra vinegar or cleaner. At this point, the original smell should be gone and you may no longer see the stain.
Use a small amount of laundry detergent to scrub away the stain. If there is still a visible stain, apply a small amount of detergent on a towel and scrub the area.
Rinse detergent or cleaner away with a damp towel.
Allow the mattress to air-dry. If possible, place the mattress outside to dry in the sun. If not, expedite the process by pointing fans directly at the wet area. Depending on the size of the original stain, you may not be able to sleep on the bed for a night while it is drying.