Every day or so I took them off, washed them in a river and put them back on. Being merino wool they warmed up and dried surprisingly quickly.
This was not my plan from the start of the walk, I somehow managed to forget a spare pair pants and a compass. I didn't notice the missing compass until I tried to get off the summit of Scafell Pike in cloud 6 weeks in - I did notice the missing pants a bit sooner.