Good to know - we’ve fixed the main bathroom toilet twice now. Meanwhile the powder room one plows on with no problems what-so-ever. It too was where the extra kitty box was when the psychotic kitty was alive. It kept him from having to go up and down stairs. The itty bitty kitty has no problem with the privacy of using the basement box.
I put in a Sharkbites water valve. Horry clap, what a little wonder. No soldering or sweating pipe. No tightening jam nuts around a soft copper pipe, praying that it won’t twist and break. Take the valve, push it on the end of the pipe. That’s it. 3 seconds. And it’s water tight forever. Even the new flex lines that connect the valve to the toilet tank now have a “twist click” nut on them, like the gas cap on your car. It hand tightens just the right amount, and it’s done.