What does it mean when one fllushes the toilet, the tank empties, the water level comes back up to its normal level and seems stable, but when one looks at it an hour later, almost all the water is gone from the bowl? The water level is just where the porcelain ends on the far side of the bowl. In other words, the opening is full of water, but the water goes no higher. .
FWIW, this is not a low-volume toilet. It's happened three times in a row.
I do have the water supply turned almost off so it normally takes a half hour for the toilet tank and bowl to fill, but it's been working like that for years.
Another interesting thing about this toilet is that just after it finishes flushing, I hear thunder from somewhere. Well it sounds like thunder or like the way the special effects man would imitate thunder during radio dramas by taking a piece of sheet meal and shaking it.
But what's strange about this is that there's another toilet in the next bathroom, back to back with this one, with only a stud and sheetrock wall in between, using most of the same pipes, and it doesn't make this noise.