Sewer lines made of PVC continuous tubing or connected clay sections each 3-4 feet long carry sewage and waste water away from homes to main sewer lines most often located in the street. To function properly these lines must be pointing downhill their entire length and must be at least relatively clear of tree roots and other obstructions, and must not exhibit settling that might negatively alter the downhill path of the line. A test to check the condition of the line by feeding a camera through the entire length costs in the neighborhood of $180 and can be conducted by a water/sewer contractor during your 3-5 business day home inspection time frame; this test is advisable even if there are no apparent problems with the sewer. I am able to provide several contractor names if you not have one in mind. The value of such an inspection can easily be seen since the remedy for a broken or misdirected sewer line requires major excavation in the yard and a $6,000-8,000 bill.