I turn the indoor plumbing on for at least 30 minutes during an inspection. If there are any issues with the septic tank, they will typically arise during the process, showing up as a leak in the yard with an accompanying odor. Home inspections are non-invasive. For a thorough, invasive inspection of the septic tank (including digging around the tank), you will need to contact a licensed septic tank specialist. To date, I have never had a client contact me with a septic tank issue after a home inspection.