My two cents is that it's acceptable to arrive somewhere dusty and dirty. I've shown up places after riding all day on dirt trails, covered in dirt, my hands oily from fixing a chain, my clothes dusty, but it's how you comport yourself after that matters. You shower if you can, and change into your clean clothes, and show the world who you are. If I were out in the wilds, it would perhaps be different, esp if it were somewhere with limited water, but getting clean when you can is the point, even if that#s after a week. if you can get clean, but don't, then that's where it all starts getting a bit hobo.