If it's extra stubborn, consider using liquid drano. That's what our owner's manual says to use. We tried it once and it was spotless afterwards. Must be the version that does not attack metal. Also, you cannot dispose of it into a septic disposal system that has an on-site drain field. You should check with the CG to see if it's okay.
You should put in 4-5 gallons of water before you start to use the toilet after you've dumped the contents. And don't skimp on water when flushing because you think the tank will last longer. Just asking for trouble otherwise. We've been a victim of a plugged tank and it's not fun to get it cleaned out. Prevention is the best cure.
