Hi Richard, in my area, we have a lot of septic tanks. I offer a visual inspection of the Septic tank. In Ohio, we need to take a state test for Septic. Ohio has great records of septic tanks going back 50 years. I have access to the state and county websites to get the site drawings, date of pumpings etc. This helps in looking for tanks etc. I include this information with the inspection report.
Make sure to use a separate agreement for both well and septic.
InterNachi offers excellent courses for both Well and Septic. Your state may offer courses also.
Good Luck