Open lids carefully, check inlet and outlet baffles and tees, file cracks or rust

https://wiki-view.win/index.php/Professional_Sewage-disposal_Tank_Maintenance_Plans_That_Will_Not_Spend_A_Lot

Open lids carefully, check inlet and outlet baffles and tees, file cracks or corrosion, and repair seals to stop groundwater invasion and exfiltration that can overload the drainfield.