I posted a similar thread a few weeks ago, but it got off into a discussion about good and not-so-good toilets, so I thought I'd start a new one to save folks from reading all that history.
Are there any other possible causes of a bowl leaking down to bone dry in 30 minutes, other than a clogged vent, or a possible leak in the internal trap itself?
Zero moisture shows up in the ceiling below.
It's a $6-800 Black Amer Std "Savona" toilet.
.....................And the Update:
Initially we thought we had a leak out of the bottom through a hairline crack................ but maybe not! BTW,
We tried the very clever idea of inserting the clear tubing through the trapway, and no difference.
The vent through the roof is totally clear.
So we pulled it out and set it up high off the ground so we could refill the bowl and observe.
What we found, blows our mind! With 16 ounces of water in the bowl there is no leak. With 24 ounces in the bowl it leaks out of the main toilet outlet with a pretty good drip drip drip. A normal bowl level for this unit is probably around 40 ounces or so, and 2-3" higher water level, than the level with just 16 ounces of water in the bowl.
I'm 99% sure, with just 24 ounces of water in the bowl, it's not leaking through the main trapway. There is a 3/4" factory hole extending toward the front of the toilet, located maybe 2" above the bottom of the round outlet at the bottom of the bowl. Looking at the toilet turned upside down, you can see that there is a small passageway coming from that front side and connecting underneath into the main bottom outlet.
Not sure the purpose of that small passageway, but I'm pretty sure that the leak is taking that route. If so, it's hard to understand, but there is a definite leak, even at very low water levels in the bowl. It's hard to imagine that it was this way when it left the factory but I guess it's possible.
Ideas still appreciated!
PS. The bone dry trapway reported earlier may have been due to some unusually high winds, encountered earlier, though now not a factor. Once the water level got way low, it was probably easy for the howling wind to pull air inside the house through the trapway up through the vent, and dry it out.