Roots, grease and the point where repair comes in
LA Sanitation says more than half of sewer backups are caused by tree roots and poured fats, oils and grease.
Grease builds up inside a line, and cleaning is how it comes out. Roots can be cleared the same way, but they get in through joints and small openings in the pipe, and clearing them leaves those openings as they were. When a backup keeps returning to the same spot soon after cleaning, the pipe itself becomes the question, and that is where an assessment for repair or replacement starts.

