You’ll have opportunities to get laundry done during the trip, either through your accommodation or at a local laundry service.
Your Group Leader can let you know the best places and times to do it based on the itinerary.
We’d still recommend packing enough essentials, such as underwear, for the trip and seeing laundry as a useful bonus rather than something to completely rely on.
Laundry is normally an additional cost and prices will vary depending on the destination.