External sewer line clogs can occur for many reasons. Sometimes, sewer line problems are due to:
Age – Over time, the soil will shift and settle. Sewer lines begin to sag as they age.
Roots – Tree roots naturally seek sources of water, so your sewer line is a prime target. Tree roots can crack and infiltrate external plumbing pipes and cause blockages.
Utility workers– You should “call before you dig,” but even professionals can accidentally cause sewer line damage if they don’t know the location of the lines.