Use septic safe paper always. Any brand and Happy Camper. In fact I put Happy Camper in the gray tanks as well. No smell from the gray tanks. If you ever had to change a gray water valve, you would know it can smell much worse the the black water. It lubericates the valve seals. The paper is broken down very fast in the black tank with Happy Camper. Unlike with the liquid stuff I used before using the "proper" RV toilet paper that is suppose to break down fast. Nothing like dumping your black water tank and see it trickle, turn on the black tank sprayer, and then pray the clog will be pushed out before something bad happens.