Toilet Leak - not flapper?

[marnold]

Our toilet tank leaks. Over time, we've replaced the fill valve, put in a new generic flapper, and I just replaced the entire flush valve with a genuine Kohler kit (83991).

Although the leak is slow, food coloring put in the tank shows up in the bowl within moments.

So... is it leaking around where the flush valve goes through the tank? If I disassemble it (again,) sand the edge of the hole in the tank to smooth it out, and maybe apple something to the bottom rubber part of the flush valve to help it seal (teflon pipe compound?) would that help?

Thoughts?
Thanks.

 

[Terry]

Do not use Teflon paste or tape on any of these parts.

Sanding the inside of the tank is a good idea, as is a good tightening of the big nut on the bottom of the tank.

Make sure that the overflow tube does not fall into the overflow tube.
There should be an air gap to prevent siphoning.