On Fri, 19 Sep 2008 11:08:43 GMT, Anagram
wrote:

The work that needs to be done is simple, and no plumber is likely to do
it wrong. All they have to do is open the clean-out, which should be
outside, near the house, possibly buried a short distance underground.
Then do a power snake in that clean-out. That will fix it.

Then you have to ask what kind of pipe your sewer is. If it's old clay
pipe, you probably have tree roots growing into it, and those are the
probable cause of the problem. The power snake will get the tree roots,
but they will grow back, if you don't do something about them. The tree
can be a long way away from the house, even across the street. Tree
roots can grow a long way underground. If a tree gets uprooted, the
roots don't look that long, but that's because they get broken when it
gets uprooted.

As for "do something about" those roots, just be sure to periodically
pour a root killing chemical down that drain, at least annually. One
poster here has a recipe he swears by; Google Groups will help you
find it.