Multiple spot repairs that each require access, equipment, labor, and restoration — and leave you with 40 feet of aging pipe between the repaired sections, or One replacement that addresses the entire line, gives you 50+ year pipe material PVC or HDPE, eliminates all current and future defect points, and involves one round of restoration instead of several. Below the 50-percent threshold, repair usually wins. Above it, replacement usually wins. Right at the line, the pipe material and remaining lifespan tip the balance — PVC at 50 percent damage is more likely a repair case the material has decades left. Clay or cast iron at 50 percent damage is more likely a replacement case the material is aging and the remaining sections will follow.
Small details often change the interpretation. Which fixture backed up first, whether more than one drain is affected, whether the problem returned after clearing, and whether there is odor or standing water all matter.
Use these notes to describe the issue clearly. A good description is often the difference between booking a narrow cleaning visit and starting with inspection or a broader sewer conversation.