toilet bowl water level question

Recently I've noticed that about 20-30 minutes after flushing, the water level in the toilet bowl drops about a half an inch and will maintain its newly reduced level. There is no leak from the tank, and no more is entering the bowl. I'm on the 2nd floor directly above another tenant's bathroom. Could some inter-play between his toilet and mine be causing this? He says there are no apparent leaks in his ceiling. Does anyone have an idea what might be causing this? Thanks.
--
alan


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*alan* wrote:

Ask him to flush his toilet (call on telephone) while you watch the level in your bowl. If the level changes or shows some disturbance, you'll know.
The venting design is supposed to prevent this type of siphon action, but it may or may not be a serious problem. There won't be any leakage of water into the building as a result.
Jim
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*alan* writes:

Crack in the trap portion of the fixture. Has to be replaced.
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after browsing fluidmaster, i read that overfilling the bowl may also be the cause. i would try removing the fill valve's rubber hose hose from the overflow tube and observe the flushed/refill water lines again on a matching timetable. then repair according to your results and desires. don't have the rubber hose extending down into the fill tube it will cause a problem of wasting water. there are excellent directions with your fluidmaster products. for all toilet stuff just go to: www.fluidmaster.com
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wrote:

It is not an overfilled bowl because that would not take 20 minutes to drain off. In a toilet, the bowl level is the same as the bottom of the trap. The only two things that could be causing a lowering of the level is a cracked trap or a suction on an improperly vented waste line.
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On Sat, 23 Feb 2008 01:20:45 +0000, *alan* wrote:

How big is your dog?
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*alan* wrote:

My first guess would be that there is a leak from the tank into the bowl through the flush valve. This is a very common problem in my experience.
You say that no more is entering the bowl but that is difficult to tell since it will maintain its level pretty well as long as the siphon action does not start. The first thing I'd do would be to turn off the cutoff valve immediately after the tank refills and then add some food coloring to the tank water. Then watch what happens to the tank's level and the color of the water in the bowl.
--
John McGaw
[Knoxville, TN, USA]
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How does that change the level of the water in the bowl? If that were occuring, the water level would be constant, but you'd here the tank refilling.
I agree with the advice that it most likely is a suctioning action in the waste system due to improper venting. If it were a leak, most likely the water would be visible, particularly because under the described circumstances, it would have to be a crack in the bowl at a level above the floor.

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snipped-for-privacy@optonline.net wrote:

You are right. I read the OP with insufficient caffeine in my bloodstream and interpreted it as a water drop in the tank not the bowl. Please ignore my post...
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John McGaw
[Knoxville, TN, USA]
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