If I was planning to do laundry while traveling, I'd check with my host ahead of time, or give them a heads-up if I already know it's okay (e.g., I know my mother is fine with my using the washer and dryer in her kitchen, but I'm still going to mention it before I pack, in case something has changed). Conversely, when my girlfriend last visited I encouraged her to pack less and do laundry here, since we now have our own washer and dryer. If something unexpected happened--some rude person in a truck splashes dirty water all over my pants, say--I'll ask about laundry facilities, and expect a friendly answer, even if it's "we generally use the laundromat down the street, would you rather just hang those to dry?"
At the moment I have an unplanned half load of laundry in, because I've been clumsy the last day or so: when I realized I'd stained the shirt I was wearing with berries, and had another shirt soaking from yesterday, I grabbed them and a pair of pants and did a cold water wash with just those, so I could easily inspect them before they went in the dryer. My dexterity doesn't magically improve while traveling, so I might yet ask to at least soak something to avoid setting a stain, though two shirts in two days is unusually bad luck.