There is no way to pre-arrange for RV pumping at Burning Man. Your only option is to try and flag down the few service trucks that patrol the city. We strongly suggest that you limit your usage of water for showers, cooking, etc. so that you do not need to be pumped while at the event.

For more information about RVs in general, including generator etiquette and RV pumping procedures, please see http://burningman.org/event/preparation/playa-living/rvs/.