I had a plumber install a new Kohler Wellworth I bought at HD. From day 1, it leaks tank to bowl, about 3-4 gallons a day (I shut off the water inlet and 10 hours later the tank was almost empty). Everything is dry - the 3 nuts on the tank, the water inlet, the floor - but the tank doesn't stay full. Any ideas? I called Kohler and they said to tighten the nuts, but since there's no leak at the nuts, would tightening them help? I don't want to crack the tank by overtightening and I'm not handy enough to remove the tank and re-install it. BTW, the plumber assembled the toilet tank to bowl on the carpet outside the bathroom, and then set the toilet on the flange - the Kohler instructions say to bolt down the bowl 1st and then attach the tank. Does this reverse order make a big difference in the tank to bowl seal? thanks much.
It may just be a bad flapper. That would be easy to fix.
It could be the chain is too tight.
It could need spraying with silicone to freshen the rubber.
There is a small chance that the flush valve is leaking past the porcelain.
but I would say that's it's 95% the flapper.
If the bolts are dry, then they should be fine.