In message , alan_m
writes

I once worked in a building where a toilet block was no longer used and
had just been piled high with "useful junk" and the door locked. After
a while people started noticing a unpleasant smell which despite
looking for deceased rodents etc. got worse over a period of weeks. The
smell was eventually traced to the disused toilet block. The water in
the toilet bowls S bends had evaporated. The near instant short term
cure for the smell was to turn on the water again and flush the loos.

grin We had exactly the same problem in the bathroom I have just
removed. Has never been used in the 16 years we have been here, but had
to top up the water in the bends to maintain the seal - the smell would
remind me, when I forgot!
--
Graeme