We volunteered for a major national park and were parked next to the camp sink which was an outside sink labeled 'For Dishwashing Only'.
We had two campers kicked out of the park. One for getting naked and taking his bath in the sink when it got dark. The other for dumping a Porta Potty in the sink. Personally, I would never use those camp sinks. The best way to do dishes when tenting is to carry your own dishpan, boil some water and do your dishes at your site. Then dispose of the dishwater appropriately depending on how the park asks you to dispose of gray water.
Another of our duties was cleaning out the firepits when a camper left. You cannot believe what they put in it. It's like the town dump. Disgusting.