On a 29-night wild camping walk last summer, I found the only thing that demanded washing was pants. Washed them in streams and stuck them in a mesh pocket or on bushes to dry. I did hit a week of rain, but had 3 spare pairs with me. In any event, no great hardship to put a pair on damp.
Still, it was a challenge I wanted to solve. So in the autumn I invested in two pairs of merino underpants. The prices of those have always put me off, but crikey they've been an amazing buy. In an experiment towards my next hike, I've worn just those two pairs ever since: and they're still like brand new. I treat them very carefully and hand-wash them in a little organic liquid soap in the sink. But on a hike I'm sure they'd come up nice just in water.
The issue with pants is smells, and merino ones solve that to a mind-blowing degree. However unhygienic one's prepared to be on the trail, there does come a point when pants have to be washed. From my experiments with these two pairs at home, I feel confident that point will be suspended for longer now. So I might just risk taking only the two pairs next time.
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On very hot days, salt stains can accumulate on my clothes, which is unsightly. But I think nothing of removing my pack and shoes and plunging fully clothed into a river before walking on. In good weather, the body is an excellent clothes horse and everything will soon dry.