Eggshells, though often considered biodegradable, may not be ideal for septic systems. They take a long time to degrade due to their calcium carbonate composition. Over time, the membrane of eggshells can create clogs in the septic system pipes and hinder proper drainage. To maintain a healthy septic system, it's best to dispose of eggshells in the trash or consider alternative methods like composting. This will help prevent potential issues and ensure the smooth operation of your septic system.