*alan* wrote:
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

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]
http://johnmcgaw.com