The first step is to sand where the bolts go down,
You may also have to remove the flush valve with the flapper.
Sand where that drops through also. I doubt it's the rubber ring.
I would guess it to be a rough casting.
I bought the toilet a month ago; had it installed by a pro. There's a slow drip from the tank bottom. I checked the tank inside around the bolt holes for irregularities, and there're none.
I noticed when unboxing the toilet that that the O-ring tank seal is mad of a spongy, open-celled foam. When I shine a flashlight between the tank and bowl I see beads of water on the ring. I suspect it is passing water slowly through itself.
I contacted Toto and they are sending a new ring, but I doubt it will fix the problem if it's of the same material.
Comments, suggestions appreciated.
Thanks, Terry. I went away for five days on a vacation and the toilet wasn't used. When I returned home the dripping had stopped and the bolt and nut were dry. Once the toilet was being used again the drip returned. This is why I suspect the tank O-ring. Any idea why it would have water beads on the outer surface?
when you put the new gasket on, sand down the area like Terry said (you're gonna have the tank off anyway, right?). The gasket material itself isnt the issue. Those types of gaskets are used all the time. One thing I do though its recommended by some not to is to put some white pipe dope with teflon on the gasket (the side that meets the bowl to form the seal). I use a pipe dope that is ok to use on plastic though. Its worked well for me for years.