I had a plumber come out 1 1/2 months ago and clear tree roots in my main sewer line. I am connected to a septic and not city sewer. I had water backup into my bathroom again after 1 1/2 months and now the plumber won't stand by his work. He says that tree roots are in the pipes again. Is it possible for tree roots to cause a complete clog after 1 1/2 months especially in the winter months or was the job not done completely last time? He said I would have to get a new sewer line in order to fix the problem.