Bowl water level drops overnight
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Vents are Free and clear roof has about 4" of snow
Jadnashua
Retired Defense Industry Engineer xxx
A few things can cause this:
- a literal crack or hole in the bowl; depending on where it is, it may just leak down the drain and not on the floor
- siphoning of a back-t0-back toilet when it operates (is there another toilet right behind this one?)
- if the winds are just right, the pressure/vacuum in the vent line can rock the water back and forth, and some of it can drain out when it sloshes the 'right' way
A blocked vent isn't likely to cause this, but improperly venting, when something else drains, could drop the level slightly.
Got a dog? They do like to drink out of the bowl!
If it were over a week or more, you might notice the level dropping because of evaporation. This is more an issue in the winter when the typical humidity levels are lower, but can happen anytime. I notice this on mine if I'm away for a week or more. Because my mother rarely gets upstairs, when I visit, I often find her toilet and shower drain nearly dry since it might be many months between visits. In the interim, there's rarely anyone up there to use that plumbing and thus, refill them.
- a literal crack or hole in the bowl; depending on where it is, it may just leak down the drain and not on the floor
- siphoning of a back-t0-back toilet when it operates (is there another toilet right behind this one?)
- if the winds are just right, the pressure/vacuum in the vent line can rock the water back and forth, and some of it can drain out when it sloshes the 'right' way
A blocked vent isn't likely to cause this, but improperly venting, when something else drains, could drop the level slightly.
Got a dog? They do like to drink out of the bowl!
If it were over a week or more, you might notice the level dropping because of evaporation. This is more an issue in the winter when the typical humidity levels are lower, but can happen anytime. I notice this on mine if I'm away for a week or more. Because my mother rarely gets upstairs, when I visit, I often find her toilet and shower drain nearly dry since it might be many months between visits. In the interim, there's rarely anyone up there to use that plumbing and thus, refill them.
Hummm
No Cracks/holes
no back to back installation toilets are on different floors
I have noticed some water movement in the downstairs bowl during high winds but not that much as to cause the water to slosh out and down the waste pipe. There would have to be lots of water movement for the level to drop by 2+"
No Dogs here
toilet never goes unused for any extended period of time at most a day. Its not an evaporation issue
If anything perhaps the builder did something improper regarding the vent when all this was installed 20 years ago.
Is there anything different in the last week, other than the toilet problem?
I hope you did not climb up there to check. That would be dangerous. Did you get your friend with a camera on his quadcopter to take a look?
Jadnashua
Retired Defense Industry Engineer xxx
It is possible to have a crack or hole in a place you cannot see without taking the toilet off and looking that would allow the level to drop. Seems you've eliminated the other causes that I'm aware of (it may not be a complete list).
I guess the definitive way to test this would be to remove the toilet, set it up somewhere on a platform where you can monitor it. Fill the bowl to it's normal level, and periodically, watch and look for a leak. It may become obvious once you look at the bottom of the toilet when removed.
Does this now happen every day? If you go through a period of not using it, does it happen every time the bowl is refilled? A leak wouldn't come and go, once it happens, it's there.
I guess the definitive way to test this would be to remove the toilet, set it up somewhere on a platform where you can monitor it. Fill the bowl to it's normal level, and periodically, watch and look for a leak. It may become obvious once you look at the bottom of the toilet when removed.
Does this now happen every day? If you go through a period of not using it, does it happen every time the bowl is refilled? A leak wouldn't come and go, once it happens, it's there.
LLigetfa
DIYer, not in the trades
1 PSI of pressure is the equivalent of 28 inches of water column, so 2 inches of water column is not a lot of pressure. I've seen pressure changes in a small room just from the door opening and closing affect the water in the bowl. If for example, an exhaust vent is frozen shut, that avenue of air pressure escaping might be closed.
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