Use vinegar to kill fleas by placing the flea-affected animal into a bathtub with warm water and adding 2 cups of vinegar to the bath. Use soap to create a lather on the animal's skin, and use the vinegar water to rinse and bathe the animal's coat.
For best results with this method, allow the animal to air dry after bathing if it is warm enough. During the bath, the fleas should fall into the water instead of clinging to the animal's fur or whiskers. Between baths, use a squirt bottle to apply vinegar to the animal's coat every day to repel new fleas.