Jadnashua
Retired Defense Industry Engineer xxx
Toto does not make the flush valves. They generally use one from Korky and one other company for their single flush, and a different one for their dual-flush models. All are fairly big companies where you can generally gets parts from any plumbing supply house, or in the case of the Korky, repair parts from Lowes on a late Saturday night when you want to rather than calling the factory and waiting. Because they are fairly generic, you could change the whole thing out if you wished with another brand. You might lose the water efficiency by doing that, but it would still fit and work.