You can fill up (and also use dump site) at Mather Campground. It's about 25 miles from Desert View. Filling stations on the way in, close to the park also offer potable water fill up. Withing Desert View, there are faucets to fill up containers, but you're not allowed to hook up. I'm sure you're aware, but will mention anyway, the site size limitations are real. We saw two sets of campers turned away because their rigs were too long to negotiate turns or fit into sites. Just an fyi...