“on empty” would mean that there is a dial setting called “empty”; so I wouldn’t use “on empty”. However, without “on” it is correct. Then, as I mentioned in my response to this question on October 11, there is (at least for a modern washing machine) a ‘rinse cycle’ which allows you to run it while empty.
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AnonymousHow would you phrase the following sentence?It isn't good to run the microwave or a washing machine (on) empty.You shouldn't run a microwave or a washing machine when it's empty.