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There are no self service laundries on RCCL ships but they have a 'stuff all you can in a bag' day for around $15 you can get lots washed for you. Dont bother to press formal wear before packing, have it pressed for a couple of $ and returned the next day.
Yes, you send them out to the laundry. They are returned the next day. Laundry costs are very reasonable.