It depends on which part of on-site you wish to go to, the part which is "behind the stage" is normally checked, but the part next where you line up to go in isn't or at least is spotty. I've been stopped at both and gotten into both.
Meadow park has a paid to use shower, cheap though (25 or 10 cents or something). They have bathrooms with running water, but the toilets are not much better than a porta john (I can't recall if they are flush or not).
There is always the river (for bathing, not the other item)
Listening to:
Chatham County Line - IV