Glad to see someone asking before just doing and causing problems down the road. The holding tanks needs to have a good enzyme living in there to do the best job with little to no odors. The rubber seals at the dump valves need care as well. Therefore, the use of caustic agents should not be used. There are cleaners made for these and I would recommend they be used. Also include the use of some valve lube (coconut oil) too keep them happy a couple times a year. Never use formaldehyde based tank additives. Once you get a good colony of enzymes you can go for a year or more without having to add anything and have no odors or clogs.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7