If you live on a larger piece of property in a semi-rural or rural area, it's probable that your home utilizes a septic system to dispose of its water waste. Septic systems typically require relatively large spreads of unimproved land to accommodate the dispersal of treated water back into the environment. The focal point of your septic system is a septic tank that probably lies below your yard. To maximize its safety and cleanliness, it's almost certain to be located outside of the foundation of your house.
The typical homeowner's insurance policy is designed to cover certain costs related to the pipes and plumbing features that reside inside of the foundation of the home. Covered incidents might include sudden breaks caused by defective or malfunctioning pipes, toilet backups caused by defective pumps or other equipment, and freeze-related water damage caused by improperly-insulated pipes. In order for any of these events to be covered under the terms of a typical homeowner's insurance policy, the claims adjuster tasked with investigating their causes must judge them to be "sudden and accidental."
As such, it's unlikely that the costs associated with repairing, cleaning or maintaining your home's septic tank will be covered by your homeowner's insurance policy. For starters, most policies specifically exempt structures or "features" that reside outside of the foundation of the home. Since the ground beneath your yard isn't technically part of your "home," your insurance company can argue that its contents have no material effect on the integrity of your actual home. Although your septic tank is probably quite expensive to maintain and repair, it's considered an "add-on" to your house rather than an integral part of its structure.
There may be some exceptions to this general rule. If your septic tank ruptures due to a defective seal, bolt or panel, some of the damage that it causes could be covered under the terms of your homeowner's insurance policy. Ironically, it's unlikely that your policy will cover the cost of repairing your tank or fixing the damage that it causes to your yard. Rather, any covered damages associated with your ruptured septic tank are liable to be confined to properties that abut yours. If your neighbor's yard becomes flooded as a result of your septic leak, your insurance provider may choose to pay for any associated cleanup and repair costs. In most cases, your neighbor will request that you file a claim after such an event.