The Other Mike wrote:
I took apart as much of the plumbing as I could which includes the
trap. The trap goes up into another pipe which is about twice the
diameter of the trap pipe that goes straight to the basement...that's
where I stopped.

Another poster mentioned proper venting....where is this venting
done?? All the pipes under the sink run into that larger pipe which
goes to the basement with nothing that looks like a vent.

there is a vent which is connected to the plumbing. It can be
connected almost anywhere but typically near the bathroom it connects
inside a wall. some call it a vent stack since it almost always exits
throught the roof and allows air into the system. If you look up on
your roof you will see an open pipe exiting the roof. the system will
not drain unless air can get into that pip. just like putting your
finger over the opening on a straw, liquid cannot escape. The vent is
usually just an open pipe so it is easy for an animal to get in there
and die or maybe build a nest. the vent can be snaked just like the
main line. You can also attempt to flush it with a garden hose. also,
when remodels are done and fixtures are added, sufficient attention to
increased venting can be overlooked. Try to snake the line under the
sink first. You can rent one at any rental store. I have had bad luck
with rentals and eventually bought a tool like this:

http://www.northerntool.com/webapp/w...4874_200114874