I have a Toto CST604CEFG toilet that has quit flushing correctly. When it was new it flushed fine. The
only way I can get it to flush is first I adjusted the screw that limits the
tank level so that the tank fills to 1/2 inch below the overflow pipe then hold
down the lever until the tank is drained. If I press the lever and don't hold it
down the flapper immediately closes. All the seals are good. There is no leaking
from the tank after it fills. I've snaked it several times thinking it might be
an obstruction. The toilet is five years old. My first thought is to replace the
flapper yet I don't see what might be wrong with it. I don't want to replace
parts unnecessarily. Do you have any ideas?

I think you are on the right track by changing the flapper.



Edited 1 times.

Yes, try replacing the flapper. They get stiff after a few years and do not work as intended.

I see many people changing to the Toto THU140S Flapper. It does not have the extra hole which allows air to remain in the flapper for a longer flush time.

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I sort of followed your idea and picked up a Korky universal flapper for Toto. This one had side holes that could be adjusted from three to one and a bottom hole that could be reduced in diameter by inserting a plug with a smaller hole. I set the side holes so only one was open and added the plug to the bottom hole and that seems to do the trick. I imagine I'm using more water than was originally intended for this water saving toilet but if I only have to flush once thats good. Thanks.