Main sewer line cleaning is commonly recommended every 18 to 24 months for a typical home. Homes with mature trees over the lateral, a history of root intrusion, older clay or cast iron pipe, or repeat backups often need it closer to once a year. Many lines with no risk factors can go longer.
The interval exists mostly because of roots. A municipal sewer department in Michigan notes that once roots enter a lateral they will likely eventually cause a blockage, and the way to stay ahead of it is to clean the line on a regular schedule. Fine roots slip through small cracks and joints, then grow into a mat that traps grease and paper, so a yard with mature trees over the line resets the clock toward once a year. Cutting or jetting the roots clears the line, but they grow back.
Rather than cleaning on a fixed date, a camera inspection of the line shows whether you need it yet and what is driving the buildup, which lets you match the schedule to your own pipe instead of an average. Professional cleaning of a main line uses a motorized cable or high-pressure water jetting; a plunger or a store-bought drain product does not reach the lateral.
Cleaning has a limit worth knowing. If roots return within a few months, or the camera shows a cracked pipe, an offset joint, or a belly where the line sags and holds water, no cleaning interval will keep it clear. At that point the lasting fix is a repair or a lining that seals the pipe, not more frequent cleaning.