How to Read a Septic As-Built Drawing

An as-built drawing looks cryptic the first time you see one: a hand-sketched plot, numbers radiating from house corners, abbreviations like ST and D-box. It is actually a simple document once you know its parts, and reading it correctly lets you walk out into the yard and put a flag on your tank lid.

The parts of the drawing

• The site plan. The property outline, the house footprint, the well if there is one, and the septic components drawn in place. North arrow and scale vary in quality; the tie measurements matter more than the sketch.
• Tie measurements. Distances from fixed reference points, usually house corners, to the tank lids, the distribution box, and the drainfield corners. Two ties from two different corners locate a point by triangulation.
• The tank spec. Capacity in gallons, material, number of compartments, and sometimes burial depth.
• The drainfield layout. Number of trenches or beds, their length, width, and spacing, and the dispersal method: gravity, pressure, chamber, and so on.
• Soil and site notes. Results of the soil evaluation or percolation test, seasonal water table observations, and the reserve area set aside for a future replacement field.
• Approval block. The installer, the inspector, dates, and the permit number that ties the drawing to the rest of the county file.

Using ties to find components

1. Pick a component, say the tank inlet lid, and read its two tie measurements, for example one distance from each of two house corners.
2. Run a tape measure from each corner the stated distance and swing an arc. Where the arcs cross is the point.
3. Probe gently or dig by hand at the crossing. Old drawings can be a few feet off; treat ties as a strong hint, not gospel.

Common abbreviations

ST or tank for the septic tank, D-box for the distribution box, DF or trenches for the drainfield, PL for property line, and BM for a benchmark reference point. When a symbol is unclear, the approval block's permit number lets you request the rest of the county file for context.

When the drawing disagrees with the yard

Systems get repaired and replaced, and not every change was recorded. If ties point at nothing, check whether a later permit exists for the property; the newest recorded document wins. If no drawing exists at all, our generator produces a free estimated design from code tables and nearby recorded systems. It is estimated, NOT a county-stamped document, but it is the practical starting point for locating what is probably there.

Related guides

• What Is a Septic As-Built Drawing?
• Septic As-Built Lookup: How to Find the Drawing for Any Property
• How to Find Your Septic Tank Lid

Get the drawing, then go find your tank

We hold more than 5.2 million recorded septic documents across 31 states, tied to parcels and viewable on the map, and we publish record-access facts for 2,388 counties across 49 states so you know exactly who holds the file where we do not.

Find your county's septic records  Open the parcel map and design tool

Common questions

What is the most useful part of an as-built?

The tie measurements. Two distances from fixed reference points locate each component by triangulation, which is how you find a buried lid without exploratory digging.

Why do the measurements not match my yard?

Decks, additions, and regrades move or hide the original reference points, and older drawings can simply be imprecise. Re-measure from the corners that still exist and treat the result as a strong hint.

What does the reserve area on the drawing mean?

Ground set aside at permitting time for a future replacement drainfield. Keep it clear; building over it can make a future repair much harder to permit.

What if there is no as-built for my property?

Check the county file for later permits first. If nothing exists, our free estimated design reconstructs the likely system from code tables and nearby recorded systems. It is estimated, NOT a county-stamped document.

Guide last reviewed 2026-09-08.