It really depends on the trip. Some trips, there's time to do laundry, and the Adventure Guides can point you to where you can get it done, other trips, you can hopefully get it done at the hotel (which is frequently expensive). The River cruises, the ship does laundry, and very reasonably. I know people who buy clothes that can be washed in the sink and hung to dry overnight. Personally, the only time I've had laundry done was on the Danube River cruise because it was SO convenient and so reasonable (it was really hot, and my clothes got pretty stinky). But, generally, I just bring enough clothes to last the trip, expecting to re-wear a few outfits, and bringing bags to put the too-dirty-to-rewear stuff in.
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