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?
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,
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.
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
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:
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.
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.
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
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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