Yadayim, Chapter One, Mishnah Four
1) If he cleansed vessels with the water or scrubbed measures with it, [the water] is invalid.
2) If he rinsed with it vessels which had already been rinsed or new vessels, it is valid.
a) Rabbi Yose declares [the water] invalid if they were new vessels.
Section one: If he used the water to clean vessels or scrub measures the water is invalid. This is because the water is considered “waste water” which shouldn’t be used to ritually clean hands. Furthermore, he has used the water for work, and therefore it can’t be used.
Section two: If the vessels didn’t need to be washed or scrubbed because they were either clean or new, then the water remains valid because it didn’t need to be used.
Rabbi Yose says that if the water was used to wash new vessels it is still disqualified since it is customary to wash off new vessels. In other words, something that is customary to do is considered work, even if it is isn’t strictly speaking necessary.