water leaving toilet bowl

[mrcaptainbob]

I'd lightly stretch some saran wrap across that hole and seal it. Then observe if it looks like it wants to get sucked in when the other toilet is flushed. That would certainly prove the venturi issue....

[pushkins]

great idea !

[karolion]

I have seen a problem like this fixed on Ask This Old House. In this episode the plumbing expert on the show brings aportable video monitor connected to a diagnostic camera, which is mounted on a flexible motorized tube, and goes down the vent stack looking for debris, dead animals, bird nests, etc. The camera is like an endoscope used in surgical procedures named with the suffix -oscopy. After, the other hosts of the show ask can this clogged vent stack be prevented and he explains that in regions where there may be freezing conditions if water was to freeze over a device made to shelter the vent stack(like you may see on a chimney) your house would build up with the pressure of unvented air and the weakest link in that chain would burst to release the air pressure. You may be able to see into the vent stack yourself with a good light source if the vent stack serves no more than 2 stories(even that is pushing it as this vent pipe may be 3-4" in diameter, up to 6" at the most;I am guesstimating here). I have this episode stored on my DVR, so if you know how to record it to a writeable cd I could e-mail it to you.

[Piper]

I know this thread is four months old, but I have to ask. Any of you ever heard of capillary action. Probably a mop string or some type of cloth or string stuck in a position over the trap wier in the closet slowly syphoning the water out.