Mix chlorine bleach with water. You only need to use a few drops of chlorine bleach in a few cups of water to kill the germs.
Put on rubber gloves and drip a rag into your bleach/water mixture.
Scrub the used mattress using the rag and bleach mixture. If there are any stains on the mattress, you might want to use a scrub brush. Try not to get the mattress too wet.
Rinse the mattress using a new rag and a bucket of clean water.
Allow the mattress to dry completely. You might want to use a wet/dry vacuum to soak up the remaining liquid.
Sprinkle the mattress with baking soda once it's dry. Vacuum up the baking soda. This will help to neutralize any odors from the mattress and the bleach.