“What additive is best for my RV holding tank?” is probably the most asked question I get, especially when I’m hydro-jet high-pressure cleaning RV tanks. Searching Facebook or YouTube will result in about as many tank treatments or advice as there are RVs. recommendations are as varied as the stars in the sky, suggesting store-bought liquids, powders, or packets, and even various homemade recipes. When asked what to use, I always answer “water”.  Seriously, water is your best tank additive, and most RV tank problems are due to not having enough water.  When you dump your black tank and close the valve, always fill at least two toilet bowls full…