Rush Locates can perform an on-site search for a cesspool that may or may not exist in Oregon or Washington using Ground Penetrating Radar (GPR) for $300. Call us today to schedule a cesspool locate with GPR.

This article describes the common ways to find a cesspool location or a septic tank location if one exists. It can sometimes find drywells that can’t be found by scoping the rain drain.

image of cesspool and sewer utilities found with ground penetrating radar GPR scan

The City of Portland hosts this document online as a downloadable PDF but Rush Locates host it online so you don’t have to download it. To get the original file click here.


Septic tanks, cesspools and seepage pits are required by OAR 340-071-0185 to be decommissioned when the systems are no longer in use. A Decommissioning Permit is required to document the decommissioning and record the location of the decommissioned septic system.

A Decommissioning Permit must be obtained when:
• A sewerage system becomes available and the facility the system serves has been connected to that sewerage system;
• The source of the sewage is permanently eliminated (e.g. a structure is demolished);
• New construction (e.g. a home, addition, garage, ADU, deck, etc.) is proposed within 10 feet of an abandoned system;
• A land division is proposed on a property with an abandoned system;
• A property line adjustment is proposed that would result in an abandoned system being located on a different lot or within five (5) feet of the adjusted property line.
NOTE: Septic Decommissioning IS NOT REQUIRED for a real estate transaction. Decommissioning is part of the negotiation between buyer and seller, and will require excavation of the existing yard.

What is an abandoned septic system?

An abandoned septic system typically consists of a cesspool OR a septic tank to either a drainfield or seepage pit.


Cesspools are typically cylinders 3 to 4-feet in diameter, approximately 15 feet deep with perforations made of either brick or pre-cast concrete rings. Cesspools are commonly found East of the Willamette River.
• Prior to the 1950’s, cesspools were typically constructed of brick.
• After the 1950’s, cesspools were typically made of precast concrete rings.


Septic tanks are rectangular in shape, commonly 5 to 7 feet long by 5 to 7 feet deep. Septic tanks were of concrete or metal. Septic tanks are commonly found West of the Willamette River.
Septic tanks drain to either a drainfield or seepage pit.
(The drainfields do not need decommissioning; only the tank &/or seepage pit require decommissioning)


Seepage pits are a cesspool with a septic tank preceding it.

How do I determine whether a property has a septic system?

If a home/building was constructed with plumbing and built prior to availability of a public sewer system, it had a septic system.
1. Go to and enter the property address in the search box.
2. Click on the Permits & Zoning button and then click the Permits button. Note the year built on the Summary page.
3. Scroll down and click on Historic Plumbing and then click on each ID link to access available plumbing records through the Historic Permit Records Viewer.

  • a. Each permit record may contain several pages. Most plumbing records have a table and narrative description on the front and a drawing on the back.
    • Printing double-sided or two records per page is recommended in order to keep the front and back pages together.
  • b. Septic systems may be indicated within the plumbing record table, narrative description or the drawing. In many cases, there will not be a record of a septic system (see page 2 for how to locate on site).

4. If the records do not clearly state DECOMMISSION FILLED, the septic system was NOT decommissioned.

Where is an abandoned septic system usually located?

Find the main plumbing vent stack (usually 4”) coming through the roof, visualize a straight line extending from the stack through the exterior foundation, and then locate and follow the original plumbing line to either the cesspool or septic tank:

• Cesspools are:
◉ Typically 10-12 feet straight out from the foundation, in line with that main plumbing vent stack on the roof.
◉ About 3 to 5 feet below ground surface (bgs) to the top, if the building does not have plumbing in the
basement, or about 8 to 10 feet bgs if it does.
◉ In general the top can be found at the depth the sewer line is exiting the building, plus 2 feet.

• Septic tanks:
◉ Vary in location (may be 5 to 30 feet from the foundation).
◉ Are typically 1 to 3 feet bgs.
**Please note that digging for and following the original sanitary sewer line is the most reliable way to find it**

Replacement Cesspools

Are usually located straight out or offset at a 45° angle and approximately 10 feet away from the original cesspool (see diagram). For example:
• A record showing a cesspool located 22 feet from a building is likely a replacement cesspool, regardless of what the plumbing record narrative may or may not say.
• Similarly, if the plumbing record shows a new cesspool in 1971, but the home was built in 1943, two cesspools will need to be located, one of brick and one of concrete.

where to find a cesspool

How do I decommission a septic system?

Step 1:

Complete and submit a Sanitation Evaluation Application and appropriate fees to:

  • In Person: Come to the City of Portland, Development Services Center, Trade Permits, 1900 SW 4th Ave., First floor, Portland, OR 97201. For Hours Call 503-823-7310 | Select option 1.
  • By Mail: Send completed application and check payable to the City of Portland, Attention: Trade Permits, 1900 SW 4th Ave., Suite 5000, Portland, OR 97201.
Step 2:
  • Locate the tank and/or cesspool/seepage pit.A. Pump out any sewage in the system (if applicable*)*A DEQ licensed sewage disposal provider is required to pump any residual solid and liquid wastes. A copy of the pump receipt is required prior to inspection approval.(Note: If the septic tank is water tight, make holes in the bottom so any ground water will drain through) B. Fill using suitable material (cannot use common soil or dirt).
    1. Suitable materials include:
      ■ 3⁄4 inch minus gravel ■ Masonry or playground sand ■ Concrete slurry
    2. If using sand or gravel, fill in lifts of 1 to 5 feet thick and water down and/or tamp for proper compaction. If a new foundation will be constructed within 10 feet of the septic system, the fill may need to be placed as structural fill and compaction testing required. Consultation with your engineer may be required.

    C. Leave the top 12-18” of the cesspool unfilled and the original pipe going to it exposed so the inspector can observe what type of material the system was made of.

    Step 3:
  • Request the inspection after properly filling the system and prior to covering (Step 2 #C)Note: An inspection is required even if the system is not located. We need to document if adequate efforts were made or if more digging is required. Leave all excavations open.

A. Call 503-823-7000 (IVR Request Line)
B. Request #842 Decommissioning inspection

Step 4:

After inspection approval, complete filling to final grade.

septic_decommissioning 04/11/17 City of Portland Oregon – Bureau of Development Services

End of Document.

Picture of Metal septic tank in yard

Want to search for a cesspool location? Call Rush Locates to help!

It doesn’t matter if you want to get a record of no tanks for the future or look for a septic service hatch we can help! Rush Locates, LLC will help you get your project right the first time. If however you have already had a search and they were unable to figure anything out give us a call. In that case being able to discover things other locators can’t is our job.

We made a page for both cesspools and septic tanks (and drywells) if you’re curious. Of course if you don’t want to read more about cesspit location and septic tank locating we have other pages.