I have been unable to find in any hardware store a flush valve for a one piece toilet . I don't know if such a valve exists and if so, how it is installed. I have replaced the "flapper" with an exact flapper but it still fails to seal properly and the water continues to run because it cannot fill the water closet or tank. Thanks for any possible answers.

 

Interesting question. I had the "same" problem. Mine ended up being the overflow tube leaking. With some aquarium silicone I was able to fix it.
Not sure if your toilet is the same as mine but I had to unscrew the whole assembly from the bottom of the tank. This consisted of a nut and a piece that held the assembly into the tank. After removal, I had to check for leaks. I had replaced 3 flappers before I finally found the problem. Reply back if you need more advice on this or other questions. Good luck.

 

Thanks for your reply. I just now found the name of the commode--American Standard is inscribed on the flush handle!! I replaced that valve you spoke of a couple of years ago with the Flush Master(?). The piece of plastic that the flapper rests on appears to be screwed into the pipe(?) inside the tank and has a big rubber washer. There are no bolts for this item. It appears to empty, or lead into, the bowl directly. At least the flapper assembly is right over that part of the bowl.
If you didn't already know it, you can certainly tell that I am not a plumber by anyone's definition. BTW, the flapper is not the conventional flapper commonly seen or used in a commode. It is not attached to a "plastic pipe" and the flapper does not have "ears" that normally attach to the "pipe". Before putting in the new "flapper" I used a piece of fine sand paper and sanded the pipe that the "flapper" rests on. Still doesn't make the seal. Help

EDIT: Forgot to add that the part that the flapper is attached to the bottom by just pushing it onto. The "part" is a crisscrossed plastic piece---two pieces really and the top piece is longer than the crossed piece and the chain from the top piece is attached to the flush handle. Hope I have described that adequately. Strange looking item in a water tank/closet.

 

Any other takers on my problem? I have secured a "disk" as a replacement for the "flapper" that isn't the conventional flapper. The disk covers the water outlet that flows into the bowl where flushing takes place but it will not completely seal off that opening to keep the replenished water in tank after flushing is finished---so I get the leak!! TIA

 

I have one piece American Standard Toilets in my house. They have been discontinued for many years but parts are still available (#47107-0070A). Try and get a model number off the inside of the tank. Check the website link below for replacement parts:
http://www.plumbingsupply.com/amstan.html

Also Brasscraft makes replacement parts for many older American Standard toilets.
-Good Luck-

 

Thanks Rainbird for the link. I looked at the site but could never open the part number. This dummy had an idea today. I put a small clamp on the disk where it is pushed onto the lower part of the flush valve. Why did I do that?
To eliminate the disk from turning when incoming water caused it to move ever so slightly. I made sure the disk FULLY covered the opening in the bottom of the tank and I then held it in place and secured the clamp. So far--no leaking!!! It seems the disk should be a bit larger to adequately cover the incoming water connection in the bottom of the tank(water closet).
BTW, I have the same "setup" in the other commode(a 2 piece commode) and now the disk is 2 years old and without a problem.
Thanks to both of you for your help.