Yes, yes, and yes.......

Before you rip the toilet out, go in the attic, crawl space, or
whatever is above there and inspect ALL vent pipes. I have seen them
rust thru from the condensation, even saw one that had a 1.5 inch vent
pipe totally disconnected from the cast iron stack. Also, check the
sink in that room for bad drain pipes. I know there is no tub in such
a small room. If all of that checks OK, then remove the toilet and
replace the wax ring. You could also have a bad vent pipe inside the
wall, which is usually right near or behind the toilet. That will
require wall removal, so check that last. One other thing. Is there a
lower roof with another vent outside the window to that room? The
odor could just be sucked into the window.

Mark

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On 5 Aug 2006 09:18:30 -0700, wrote:

Make sure the tub and sink traps are not empty when this is happening.
Sometimes wierd things happen with the vents, debris , strange winds ,
etc because not all plumbing jobs are optimal.
In addition in a very old house I have seen vent piping rusted through
and leaking sewer gases to the interior.
I doubt it is the toilet, but it could be the soil stack that rises up
through the roof .
Because it is intermittant my guess is some event is sucking the water
from tub or sink trap.

Ike wrote:
I only ask this question because I hate the thought of doing it and am
not sure it is necessary. We have a toilet on the second floor. It is
in a true water closet -- 3' x 5'. There is no sign of any leakage
around the toilet or on the first floor ceiling. However, once in
awhile, mostly when it is very hot upstairs, this tiny bathroom has an
unpleasant odor to it. This seems to happen even when to bowl has been
thoroughly scrubbed and sanitized. I am considering pulling the bowl
to see if the wax ring has some seepage. But, before I do, is it
possible that this odor is coming from a vent someplace or from the
sewer line?