“What additive is best for my RV holding tank?” is probably the most asked question, especially when I’m hydro-jet high-pressure cleaning RV holding tanks. Searching Facebook or YouTube will result in about as many tank treatments or advice as there are RVs, suggesting store-bought liquids, powders, or packets, and even various homemade recipes or geo methods. And the dreaded “Here’s what I use, never had a problem”. When asked what to use, my answer is twofold: “Water” is first.  Seriously, water is the most important tank additive, and most RV tank problems are due to insufficient water.  Second is to use a “Probiotic Treatment”. When you dump your black tank…