Vis a vis "green", nothing used by humans or animals is green. It will impact the environment somehow because food & water is needed to be hydrated and fed; urination and defecation is the result of drinking and eating. Washing sends detergent into the system. Water use impacts availability: just ask Californians. RVing itself uses fossil fuels. There's always trade-offs.
That said, we use paper towels to wipe out our cast iron. The oil soaked towel is then a terrific fire starter for charcoal. We save them in a ziplock bag. No water used; no trash and no chemicals to start our charcoal.
