overflowing toilet

Right, this is strange, but I'm not a plumber. Toilet flushes fine with a ⅓ of a bucket filled with water. It's not clogged. Adjacent bathtub drains fine. Cistern and bowl fill, but at the same time, but not always — this is when the toilet overflows. Flapper is intact, and doesn't leak into...

Hello out there! I am knee deep in , well, you can guess. My 62 y/o split level has two upstairs bathrooms and one lower level bathroom/laundry room. For years, at least twice/yr, the bottom toilet overflows, the plumber comes and snakes the main line. The rest of the time, this toilet...