Water, water, and water. I never use chemicals except in very warm areas where we sit for a while or are storing it. Kind of like putting perfume on a pig............... chemicals left on for a long time likely do help but not much for a weekend.
Always dump when at least 2/3 full, even if that means ADDING water before you dump. Use a tank sprayer if you have one and if not, get a wand sprayer and use it a couple of times a year if you feel compelled. With enough water, almost all solids will be pulled out of the tank.
Always keep at least 2 gallons of water in your tank (for a large tank) to keep any residue from drying and turning into a concrete like disaster. Emptying occasionally upon arrival also means all has been well sloshed around and ready to exit.
This is one of the joys of RVing but it really is not rocket science. It is a holding tank, not a septic tank. Do NOT use Drano or any other harsh chemical as it can cause damage. Happy camping!