Ever wish you could turn off the water supply at the toilet? I did and finally cured MY problem. I added a 1/4 turn ball valve at the back of the toilet.
Reason for the mod is you can dump the water from the toilet and not have it try t fill it back up. By not having water in the toilet you can get a good scrubbing of the ball and seal.
Be sure to use automotive gasket maker on the threads and let it set for several hours before turning water back on. Don't over tighten as they are plastic threads.
Dernord 1/2" Stainless Steel (304) Mini Ball Valve NPT FxM Thread With Stainless Handle $14.95 AMAZON