"... In addition, you must frequently inspect the outside of the container for signs of deterioration, discharges, or accumulation of oil inside diked areas. Records of inspections and tests kept under usual and customary business practices satisfy the record keeping requirements of this paragraph...."
Most SPCC plan writers interpret the inspection requirement as daily for facilities that are manned on a regular basis, and set some other frequency, typically weekly or monthly, for unmanned locations. This can be integrated into daily inventory documentation, inventory reconciliation, and solids/water monitoring.