We recommend Happy Campers without reservation, and we suggest you buy the bigger container than we have linked here to save money. We used this holding tank solution in both of our tanks – gray and black – from the start and have never experienced the troubles that you often see discussed in RV Facebook groups. No unpleasant odors or sewer smells, even in extreme temperatures. The best part? It liquifies waste solids and helps to break down tissue paper, so you can use the bathroom as you normally would and still maintain all of your tank level sensors in fine working condition. And no terrible sights or smells when you dump! Don’t waste time on DIY solutions or other products that don’t work. It’s like a tiny scoop of magic, solving your smelly issues in no time.