I go to flush the toilet in the morning and the tank is empty. I lift fill valve to refill tank. It stops filling to proper level and I am able to flush the toilet. After a half-hour, I notice water level in tank has gone down about half a centimeter. No sound and level in toilet bowl does not change. After 8 or so hours, tank is completely void of water and we're back to square one. What is going on?

It is a common problem. Water is leaking through the rubber flopper. Replace flopper. That will stop the leak.

Advice: Close water to the toilet, remove old flopper ( the rubber "closer" in the middle, bottom, of the tank ), take it with you to the store and get exactly the same flopper. Otherwise, you may be going to the store twice.

Hope that helps

Milo

Also, run your fingernail around the seat. If you find rough spots or nicks replace the flush valve.. Good luck, Tom

Yep I agree with the masters, good luck.

John