Ok - so many posts here, it's mind blowing. Here's exactly what's happening - tank is filling up just fine... water stopping exactly 1/2" under overflow tube. Flapper is shutting perfectly - no water leaking. It's the bowl water that's messed up. Toilet has been working perfectly for 12 years. We now flush it - the water rises to about an inch below the top of the bowl and then VERY SLOWLY flushes until all the water goes out and fills back up with very little water. If I use a plunger while it's flushing, the water goes down just fine. We have bathrooms back to back with the toilets using the same main sewer drain. Other toilet is flushing just fine so it's not in the main sewer line. I've tried snaking the toilet too. That doesn't help. The ballcock and flapper are only 18 months old and have been working perfect up until 2 days ago. Any ideas?

I know you said you snake it but you have something partially blocking either the toilet itself or the drain pipe between the toilet and the main stack.
What is suppose to happen is that you flush, the water in the tank rapidly over fills the bowl and starts the siphoning action that empties the bowl. While that is happening more water is flowing into the bowl. When the bowl is emptied air is drawn into the drain pipe breaking the siphoning action. If emptying of the bowl occurs to slowly, the water that is suppose to refill the bowl goes out with drain. The blockage must be in the toilet or the drain pipe to the main stack or the other toilet would do the same thing.

To test my logic, flush and hold the handle down until the flush is complete. The water that refills the bowl is proportioned to the water that refills the tank. What you are doing is holding the flush valve open until the flush is complete. Then the bowl will have the correct amount of water to properly refill.

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Originally Posted by hkstroud

I know you said you snake it but you have something partially blocking either the toilet itself or the drain pipe between the toilet and the main stack.
What is suppose to happen is that you flush, the water in the tank rapidly over fills the bowl and starts the siphoning action that empties the bowl. While that is happening more water is flowing into the bowl. When the bowl is emptied air is drawn into the drain pipe breaking the siphoning action. If emptying of the bowl occurs to slowly, the water that is suppose to refill the bowl goes out with drain. The blockage must be in the toilet or the drain pipe to the main stack or the other toilet would do the same thing.

To test my logic, flush and hold the handle down until the flush is complete. The water that refills the bowl is proportioned to the water that refills the tank. What you are doing is holding the flush valve open until the flush is complete. Then the bowl will have the correct amount of water to properly refill.

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Thank you! With getting it down to where you thought the problem was, I decided to dump some enzyme drain opener that a plumber had left with us when our sink drain was clogged a couple of years ago. I dumped it into the bowl and down the overflow pipe and left it sit for a few hours. Flushed it and it worked beautifully the first attempt. Have flushed it a few times since and everything is back to normal. Thanks again!

And we thank you for the update. Good luck, Tom