Human: How do I know when my septic tank is about to back up? Assistant: 
The best way to tell if your septic tank is about to back up is to look for signs of a buildup in the tank, such as an increase in the amount of foul odors or gurgling sounds coming from the tank. You can also check the water level inside the tank and compare it to the water level outside the tank. If you notice any changes in these levels, then it could be a sign that your septic tank is backing up.