Most Columbus-area residential tanks are 1,000-1,500 gallons (Delaware/Licking/Fairfield county codes). Local contractors confirm size during inspection; older tanks (pre-1980) may be smaller and need upgrading.
More detail
County code dictates minimum tank size by bedroom count. Delaware County requires 1,000 gallons for 1-3 bedrooms and 1,500 gallons for 4+ bedrooms. Licking and Fairfield follow similar schedules. Union County allows 750 gallons for 2-bedroom systems but requires 1,000+ for 3-bedroom and up. Pre-1980 Central Ohio tanks are commonly 500-750 gallons, which by current code is undersized for typical household occupancy. Undersized tanks fill faster, require more frequent pumping (every 1-2 years vs 3-5), and produce poorer-quality effluent. When the tank is replaced (during repair or full system replacement), counties require upsizing to current code; partial work on the existing tank can typically continue at original size if the system is otherwise functional. The on-site inspection includes tank capacity verification and code-compliance assessment. Columbus pre-1980 tank reality: many smaller older tanks (500-750 gallons) are still in service in older Delaware County and Licking County homes. They work but require more frequent pumping (every 1-2 years for a household of 4) and produce poorer-quality effluent that accelerates drain-field wear. When such a tank reaches end of life, replacement to current-code size (1,000+ gallons) is required.