After I flush the commode, the water level in the bowl fills to the appropriate level and then in a couple of minutes, the water will slowly drain out of the bowl to only about 2 inches deep. There is no sign of a leak and the water level always stops at about two inches deep in the bowl.
There are three things that can lead to your problem: –cracked bowl that leaks water; –faulty waste vent; –siphonage due to material (cloth/paper/etc.) caught in the bowl trap.
The first you’ve apparent excluded…the leaking water will soak the floor under the toilet. Make sure that isn’t happening.
The second usually causes the water to be sucked out of the bowl with a gurgling sound in a series of “waves.”
The third usually siphons the water from the bowl more slowly and continuously than would a blocked or missing vent.
The first thing you should do is plunge the toilet, then run it through with a closet auger. If that doesn’t work, snake the drain line from the vent on the roof (you better have one…if you don’t, that’s your problem!). If that doesn’t work, remove the bowl and snake through the closet bend.
What it sounds like is you have a crack inside the bowl and the water drains to that level and quits. Take up bowl and take it outside and set it on blocks and fill it with water and see if it drains out.