Septic Tank Size for a Target Pump-Out Interval
The inverse of the pump-out-interval tile: the tank working volume that puts a target number of years between pumpings, tank = years x people x accumulation / fill. A 4-person home at 30 gal/person/yr wanting 5 years needs ~1,820 gal. State minimum tank sizes by bedroom count usually govern.
Formula and source
Tank working volume = target_years x occupants x accumulation_per_person_per_year / fill_fraction (the inverse of years = tank x fill / (people x accumulation)).
USEPA Onsite Wastewater Treatment Systems Manual (EPA/625/R-00/008); university onsite-wastewater extension pumping-frequency guidance, by name.
Audience
This tile is built for plumbers and the adjacent professions in the Plumbing and Gas group. The interactive calculator runs entirely in your browser. No account, no fee, no advertising, no tracking.
Related tools
Posture
Rough Logic answers the math question the working professional asks on the job. The site is a calm, fast, ad-free, account-free, ever-free reference. It does not interpret code. It does not replace the licensed professional. It does not store your inputs. The Authority Having Jurisdiction governs all installations and inspections.