We always use the bathroom sink. I don't want to prepare my food in the same sink that I wash my hands in after using the bathroom but that is just me and everyone is different. I brush my teeth in the bathroom and use the sink there for that also. When we are in water conservation mode we fill the sink with water when wetting down and then lather up and then use the water in the sink to rinse off with. Saves a lot of water.
I have a dry bath now but when we had our camper it was a wet bath and still used it the same way.