it sounds to me like when someone redid the plumbing they didnt vent the
stack through the roof properly and you may simply find an open vent pipe in
the wall.... this is somewhat common with do it yourelf plumbers who
realize too late they are going to need to put a hole in their roof.

something to look into anyway..


There's a curious smell in the
between-wall spaces under the bathroom that I assume is fecal in nature
but
doesn't exactly smell like the 'real thing' [or Coke].

The pipes for the toilet are at this point ABS.