# Septic Tank: Building Code Definition

> How the IRC 2009 define septic tank, where the wording differs, and which chapters depend on the term.

- Canonical: https://harth.build/resources/glossary/septic-tank/
- Last updated: 2026-09-07
- Data source: Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The [ICC code library](https://codes.iccsafe.org/codes) publishes the current model text and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) show which edition a jurisdiction has adopted; those sources control.

## Key facts

| Fact | Value |
| --- | --- |
| Defined in | IRC 2009 (2009 editions transcribed in this corpus) |
| Primary source | IRC 2009 Definitions (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 10 (counted across the codes hosted here) |
| Wording identical across codes | Single code (compare before citing one code's wording under another) |

## Direct answer

Septic tank is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “A water-tight receptor that receives the discharge of a building sanitary drainage system and is constructed so as to separate solids from the liquid, digest organic matter through a period of detention, and allow the liquids to discharge into the soil outside of the tank through a system of open joint or perforated piping or …” No other I-Code in this corpus defines it, so the IRC 2009 definition is the one to work from. The term is used in 10 chapters of this corpus, most often in Tanks (IPC 2009), Materials (IPC 2009), Water Supply and Distribution (IPC 2009). These pages transcribe the 2009 model text; verify the definition against the edition and amendments your authority having jurisdiction has adopted.

*Content and cited inputs reviewed by [Scott Barrington](https://nz.linkedin.com/in/barrington), Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.*

## What does this term mean?

**Septic Tank** — IRC 2009, Definitions:

> A water-tight receptor that receives the discharge of a building sanitary drainage system and is constructed so as to separate solids from the liquid, digest organic matter through a period of detention, and allow the liquids to discharge into the soil outside of the tank through a system of open joint or perforated piping or a seepage pit.

![Labeled code-term definition diagram: Septic Tank: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/septic-tank/diagram-1344.webp)

*How the IRC 2009 define septic tank, where the wording differs, and which chapters depend on the term.*

## What must be verified before using this guidance?

**Septic Tank** is defined once in this corpus, in the [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) chapter of the International Residential Code (IRC) 2009:

> A water-tight receptor that receives the discharge of a building sanitary drainage system and is constructed so as to separate solids from the liquid, digest organic matter through a period of detention, and allow the liquids to discharge into the soil outside of the tank through a system of open joint or perforated piping or a seepage pit.

## Where septic tank is used in the code

The term appears in 10 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.

| Chapter | Code | Mentions |
| --- | --- | --- |
| [Tanks](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/tanks.md) | IPC 2009 | 19 |
| [Materials](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/materials.md) | IPC 2009 | 4 |
| [Water Supply and Distribution](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/water-supply-and-distribution.md) | IPC 2009 | 4 |
| [General Plumbing Requirements](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/general-plumbing-requirements.md) | IRC 2009 | 3 |
| [General Regulations](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/general-regulations.md) | IPC 2009 | 2 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 2 |
| [Definitions](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/definitions.md) | IPC 2009 | 1 |
| [Inspections](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/inspections.md) | IPC 2009 | 1 |
| [Mound Systems](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/mound-systems.md) | IPC 2009 | 1 |
| [Soil Absorption Systems](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/soil-absorption-systems.md) | IPC 2009 | 1 |

### The term in use

How the code actually writes about septic tank, quoted from the 2009 text hosted here:

> The secondary compartment of a septic tank shall have not less than a capacity of 250 gallons (946 L) and not more than one-third of the total capacity.

— [IPC 2009 §802.2](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/tanks.md)

> Joints between the concrete septic tank and the tank cover and between the septic tank cover and manhole riser shall be tongue and groove or shiplap-type and sealed water tight using cement, mortar or bituminous compound.

— [IPC 2009 §504.2](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/materials.md)

> BUilding sewers that connect to private sewage disposal systems shall be a minimum of [NUMBER] inches (mm) below finished grade at the point of septic tank connection.

— [IRC 2009 §P2603.6.1](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/general-plumbing-requirements.md)


## The terms septic tank is built out of

The definition above leans on 5 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what septic tank covers:

- **[Drainage System](https://harth.build/resources/glossary/drainage-system.md)** — IPC 2009: Piping within a public or private premise that conveys sewage, rainwater or other liquid wastes to a point of disposal.
- **[Building](https://harth.build/resources/glossary/building.md)** — IBC 2009: Any structure used or intended for supporting or sheltering any use or occupancy.
- **[Receptor](https://harth.build/resources/glossary/receptor.md)** — IRC 2009: A fixture or device that receives the discharge from indirect waste pipes.
- **[Liquid](https://harth.build/resources/glossary/liquid.md)** — IBC 2009: A material that has a melting point that is equal to or less than 68°F (20°C) and a boiling point that is greater than 68°F (20°C) at 14.7 pounds per square inch absolute (psia) (101 kPa).
- **[Piping](https://harth.build/resources/glossary/piping.md)** — IRC 2009: Where used in this code, “piping” refers to either pipe or tubing, or both.

## Septic Tank: what to open, and in what order

Every row is a document this term depends on. The [ICC code library](https://codes.iccsafe.org/codes) and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) cover the middle rows.

| Check | Where | Confirmed |
| --- | --- | --- |
| Read the definition in the adopted IRC | Definitions | |
| Re-check the requirement that uses it | Tanks (IPC 2009) | |
| Re-check the requirement that uses it | Materials (IPC 2009) | |
| Re-check the requirement that uses it | Water Supply and Distribution (IPC 2009) | |
| Re-check the requirement that uses it | General Plumbing Requirements (IRC 2009) | |
| Confirm the dependent definition | Drainage System | |
| Confirm the dependent definition | Building | |
| Confirm the dependent definition | Receptor | |
| Local amendment to any of the above | Jurisdiction's amendment list | |

**A research aid, not a code determination.** The authority having jurisdiction decides which edition and which amendments apply.

## Where can you explore related guidance?

- [Explore all glossary guidance](https://harth.build/resources/glossary.md)
- [Drainage System: Building Code Definition](https://harth.build/resources/glossary/drainage-system.md)
- [Receptor: Building Code Definition](https://harth.build/resources/glossary/receptor.md)
- [Building: Building Code Definition](https://harth.build/resources/glossary/building.md)
- [System: Building Code Definition](https://harth.build/resources/glossary/system.md)

## Sources and method

Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The [ICC code library](https://codes.iccsafe.org/codes) publishes the current model text and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) show which edition a jurisdiction has adopted; those sources control.

### Source links

- [codes.iccsafe.org](https://codes.iccsafe.org/codes)

- [iccsafe.org](https://www.iccsafe.org/advocacy/code-adoption-maps/)

## Frequently asked questions

### What is the code definition of septic tank?

The International Residential Code (IRC) 2009 defines it in Definitions as: “A water-tight receptor that receives the discharge of a building sanitary drainage system and is constructed so as to separate solids from the liquid, digest organic matter through a period of detention, and allow the liquids to discharge into the soil outside of the tank through a system of open joint or perforated piping or a seepage pit.” The 2009 model text is reproduced here; the definition that binds your project is the one in the edition your jurisdiction has adopted, as amended locally.

### Which parts of the code depend on septic tank?

In this corpus the term is used across 10 chapters, led by Tanks in the IPC 2009. Those are the sections whose scope moves if the definition is amended locally, so read them together with Chapter 2 rather than on their own.

### What is the minimum distance between a septic tank and a building?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “A water-tight receptor that receives the discharge of a building sanitary drainage system and is constructed so as to separate solids from the liquid, digest organic matter through a period of detention, and allow the liquids to discharge into the soil outside of the tank through a system of open joint or perforated piping or …” It is defined in IRC 2009. It is not the same as Building, which the IBC 2009 defines separately as “Any structure used or intended for supporting or sheltering any use or occupancy.” Because it is a defined term, whatever the adopted edition says it means is what every section using it means — so check Chapter 2 of that edition and any local amendment before relying on this wording.

### What are the requirements for a septic system in Florida?

System is a separate defined term. The IFC 2009 defines it as: “An assembly of equipment consisting of a tank, container or containers, appurtenances, pumps, compressors and connecting piping.” That is not the same as septic tank, which the IRC 2009 defines as “A water-tight receptor that receives the discharge of a building sanitary drainage system and is constructed so as to separate solids from the liquid, digest organic matter through a period of detention, and allow the liquids to discharge into the …” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.

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