One of our toilets started leaking a few weeks ago; it’s a Toto, so I got the Korky 2023 adjustable flapper and set to work. My particular toilet needs the “flapper plug” to be inserted in the flapper, but it wouldn’t stay in place. I installed the flapper without the plug and it helped, but it wasn’t a real fix.
I called Korky to complain, and they sent me a complete replacement flapper kit. This time, the plug stayed in place in the flapper. I installed the new flapper today and…the toilet still leaked.
A web search on “toilet leaks after replacing flapper” took me to an article at I’ll Just Fix It Myself with six possible causes and fixes. The toilet is a one-piece model, so I didn’t have to worry about t-bolts, and tightening the flange bolts didn’t help. The drain didn’t seem clogged, but I decided to try to unclog it anyway. I followed the instructions at Mr. Rooter, and it worked!
I don’t understand the physics of toilets; in particular, I don’t understand how the toilet can flush with a clogged drain, nor how a clogged drain can keep the flapper from sealing properly. But I guess it’s like magic – if you perform the invocation properly, you get the right result whether you understand it or not!