Myth No.7: I'm buying a house and don't think I need a septic inspection
There is only one way to find out if a system is working properly and that's with a camera inspection.
Monitoring the drainage within the septic distribution trench is important to consider the drainage characteristics of the effluent exiting the tank. That's why the hydrostatic load testing and dye testing is performed from the outlet of the septic tank.
Flushing the toilets and running water isn't going to tell you if the septic is working fine or not.