Typically, an appliance is considered to be an asset if used in/for the production of income. Being in a rental, it's used for the production of income. So it would be treated as an asset, classified as an appliance and depreciated over 5 years.
However, a washer does meet the criteria for the safe harbor de-minimus election if it's cost is less than $2,500. Personally, I don't know anyone who would spend more than $2,500 for a washing machine in a rental property. So under safe harbor you can just expense the item and enter it's cost in the rental expenses section as a miscellaneous expense. That way, you're done with it and don't have to deal with it again on your taxes if/when it breaks in the future, or if you sell the property.
