First and foremost, use plenty of water every time you use the toilet. After dumping, whether you add some home made concoction or store bought chemicals, add several gallons of additional water. If sensors don't indicate empty after dumping, tanks must be rinsed out internally, some pre-installed tank flush kits might work but nothing does the job as well as a tank wand. A properly sealed and vented black tank should not emit odors other than when flushing, using deodorants just treats the symptoms but does not resolve the issue.