I have had a plumber come out several times in the last few months to snake out the drainage traps. In heavy rains it backs up. I have also put Root Killer in the two trap areas ( sorry I don't know the technical name). I have had 1/2 of my backyard opened up and placed in new piping because the roots had busted the old clay pipes. I am still having trouble. I don't want to tear down my 2 car garage to check the pipes near the city sewers and alley .Any other suggestions?????? Help!!!