Method
How we check our numbers
Every number on this site has to be able to answer one question: where did you come from? This page is the receipt book.
Tank sizes: the rulebook, not other websites
We read each state's septic rule in its official code — the administrative code, the health department's published appendix, the state register — and transcribe the table, formula or flow rule ourselves. Each state page carries the citation (for example, Ohio's OAC 3701-29-12, Florida's Rule 64E-6.008 Table I) and a link to the official text, plus the date we checked it. If a state has no statewide table (Michigan), we say so and show a named county's real table as an example instead of inventing a state number. If a size is derived (Pennsylvania's formula, Missouri's 6-bedroom formula), the page says "worked from the code's formula."
Why the fuss? Because when we compared the most popular online chart against the official rules in nine states, not one state matched its own rulebook in full — and two states with completely different rules were displayed with the identical table. Copied charts copy errors. We would rather publish ten states we verified than fifty we didn't, so states are added only after the line-by-line check.
Costs: assembled from priced parts, labeled by strength
There is no official price list for a septic system, so we build the estimate the way you'd build a bill: soil test, permit, tank, drainfield material, fittings, labor. Every line in the estimator carries one of four labels:
| Label | Meaning | Examples on this site |
|---|---|---|
| Published price | A price list or fee schedule anyone can open | Tank prices from precast yards' and retailers' published lists (a 1,000-gal concrete tank at $1,410–$1,530 from two precast price lists); permit fees from county schedules ($600 in Johnston County, NC; $1,729 in Sacramento County, CA) |
| Published guide range | A range published by cost-guide publishers, from their project data | Soil evaluation $750–$1,900; pipe-and-gravel field material $1,500–$4,000 |
| Thin sample — approximate | Few public prices exist; we say so on the line | Aerobic units ($4,000–$8,000, dealer-sold, no shelf price); fiberglass tanks (one dealer's list plus guide ranges) |
| Our estimate | Modeled, not sampled — labeled as an estimate | Excavation & labor. There is no shelf price for labor; we estimate it from itemized project build-ups (roughly 40% of the total) and scale it by region |
Two presentation rules keep the estimate honest. First, we show the lower two-thirds of the assembled band: stacking the top of every line's range overstates real quotes, because no job is worst-case on every line. Second, partial jobs are priced from their own lines — a tank-only replacement is never just a slice of the full-system price.
One more thing we found while checking: even careful secondary sources contradict themselves — we found a cost build-up whose printed totals don't match its own itemized rows, and industry summaries claiming labor is "50–70% of total" next to itemized examples where it is about 40%. Where sources disagree, we follow the itemized numbers (the ones that can be re-added) and tell you here.
Freshness
State rules are re-checked yearly and whenever a state announces a change (North Carolina rewrote its rules in 2024; Pennsylvania has a draft revision circulating). Retail price anchors are re-checked every six months; county fee schedules yearly. The check date is printed on every page. If you spot a number that disagrees with a current rule or price list, tell us via the contact on the about page — corrections with a source link get fixed first.