The water in the toilet bowl drains out to its lowest level in approximately 15 minutes after flushing. I replaced the flapper, but the problem continued. I then purchased a kit to replace all seals between the tank and the bowl as well as the mechanisms in the tank. The toilet flushes and the level in the tank and the bowl fills to where it should be, but the water still drains out of the bowl. The water level in the tank does not change when the water drains out of the bowl. The house is all one level. The other toilet and the rest of the fixtures work fine. The bowl drains even when no other fixture is in use. When the house was purchased, the inspector said there was no leaks under the house. I have looked under the house and found no leaks.

At first id say adjust the float screw, but if the bowl water runs out , I really don't know, is taking it back an option, cause I would

Non-specific solution