Hi all,

Leaky toilet.  Leaks water from the tank into the bowl.  Have replaced the ballcock, and have been through two flappers now.  Scrubbed the bottom of both flappers (one had mineral deposits, one was new) and the bottom of the drain that the flapper rests on; said drain feels smooth to my fingers and doesn't appear to have any chips or holes in it.

If I drain the tank by leaving the flapper open and the water off, no leak.  As soon as I close the flapper, even with a tiny bit of water, leak.  

I believe the culprit is the seal between the flapper and the drain below, but I cannot see how or why (new flapper and drain edge does not appear to be damaged).

Only other thing I can think of is there is a hole or chip in the overflow tube way down below, near where the lowest water level would be.

Even if I press down firmly on the closed flapper (effectively pushing it into the drain hole, closing it as hard as I can), there is still just the ever-so-slightest dripping of water.  

End result is that, after about ten minute, the tank is completely empty of water and flushing requires two flips of the handle.

Any advice?

I would just throw it out and buy a new toilet.  You should be able to get one for under $100.  Probably not worth your time to keep buying parts and messing with it.

JB Weld.  

Drain the tank completely and let it dry overnight.

Put tape on the bottom side of the flapper.

Mix up some JB Weld and smear is around the rim of the drain hole.  

Lightly press the flapper until some JB Weld flows out from underneath.

Let is dry and see if it seals.  You might need to use some 150 grit to even it out.

Good luck.  

Instead of replacing the flapper why not use a flush valve repair kit.  Had a similar problem as you so I bought the kit for under $10 and used the plastic ring with silicone like the instructions showed and it was good as new.

If by pressing down on the flapper you still have the drip, and the seat face that the flapper seats against feels smooth and free of defects, and build-up, then the flush valve is the next step.

This statement I don't understand, why two flips?

How old is the toilet? If it has much age on it, I too would replace the toilet.

Replace the overflow tube and flapper seat assembly.

Had a similar problem.  Toilet was made by Gerber and found a flapper made just for a Gerber toilet.  Worked!  Landlord had a plumber in to fix it the first time and I got tired of the constant refilling every few hours.