I have an upstairs toilet for which the bowl will mysteriously drain over the course of 4-6 hours.
I suspect that something in my venting is causing the the bowl to siphon dry but I am unsure about how to test this.
The flange seal does not leak and I have replaced the toilet. This toilet is situated close to the stack and where the stack exits the roof. A tub and sink share the same drain. The attached sink has a supplemental vent that exits the roof within 10 feet of the stack.
I have an identical toilet situated downstairs and connected to the same stack and drain – this one works properly.
Any ideas ?