Pretty much every campsite on west coast trail has ample water, along with ocean, and there lots of opportunity to give the pants a good rinse and scrub in the gravel/sand where it goes into the ocean. You might get muddy during the day but it's not too difficult to give it a good rinse once you get into camp, heck, slip your boots off and go for a quick wade and scrub. As long as you're wearing nylon pants that mostly dry quick it's not a big deal.