I am aware that in Yosemite Valley, and with a backcountry permit one can stay in the North Pines "backpacker's campground" one night before and/or one night at the end of a trip. I also know that it costs $5 per person, which is paid to a box also in the "backpacker's camp." So where exactly is this camp? It would be helpful to know which "public / numbered" campsite it is across from or near.
It's beyond the northwest corner of the north pines campground, across a small bridge. It's not at all marked, there's no signs or anything pointing your way, and it doesn't appear on most maps, which probably is intentional, to prevent the car-camping masses from driving their RV's into it :)
Basically, just walk to the back of the north pines campground, and keep walking until you hit water, then look for the bridge. Unfortunately, there's no shuttle stops close by; I had to walk there from the trailhead parking, which is about a mile.
The campground has bathrooms and running water, including a potable water spigot. There's about 20 or so camp spaces, each can hold 2 or 3 tents. So it gets a little crowded, but it's a pleasant place. I made a lot of friends there, swapped a lot of stories.