With a septic system, all water that runs from your house, including the wastewater from the kitchen, goes into your septic tank. And when you have a garbage disposal, the amount of solid waste that goes into the tank is significantly increased.
While garbage disposal, in reality, is meant to dispose of the waste such as leftover food on your dishes, you should be extra careful if you have a septic tank. It is recommended to put everything you can into the trash can instead of into the garbage disposal. This includes all solid food and waste, as well as grease.
Otherwise, your main drain line and the septic tank will eventually back up and overflow, causing a significant and costly mess in your backyard.