Where To Look for a Septic Tank When Its Location is Unknown InspectAPedia® -
How do I find the septic tank?
Just where should you look for the septic tank? Noticing areas where it would have been possible to place a septic tank on a property can help find lost septic tanks whose location is unknown.
Where to look for the septic tanks, septic tank covers, or septic tank cleanout lids
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Septic tank location guide: this document provides suggestions and procedures for finding a septic tank when its location is unknown. When the septic tank needs to be pumped, a regular
maintenance task, the cost of that service will be less if the property owner found the septic tank location and perhaps even uncovered the
septic tank pumping access cover. Other reasons to find the septic tank include inspecting and testing septic systems
when buying a home or for safety, to assure that the septic tank cover is in good condition.
This article tells us how to locate a septic tank when it's placement is not already known or when the location of the septic tank is not visually obvious. Videos showing how to find the septic system, septic tank, & septic drainfield are at SEPTIC VIDEOS. Also see Drainfield Location - how to find the leach fields.
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This document is a chapter of Inspecting, Testing, & Maintaining Residential Septic Systems an online book on septic systems.
WHERE TO LOOK - Just Where to Look for The Septic Tank
Start looking close to the house wall - perhaps 4 ft. away. Tanks are often buried close to a building because of the convenience
of excavation during original construction, and to avoid unnecessary piping costs to a remote tank. Building codes
typically require that the tank be located 10' or more from the building so 4' is a bit close but at some old properties
we've found the septic tank right next to the foundation wall of the house.
Look at the site itself for obstructions that might have forced the excavator to put the tank into a more remote location,
such as large rocks and boulders, streams, property boundaries, wells, similar site features.
Our SEPTIC VIDEOS show how you can walk a property to find areas that are likely or unlikely to contain the septic tank or drainfield.
In the photo at page top we saw a very rocky hill with thin soil, making the probable septic tank location down in the distant, flat, lower yard. The septic tank was found to the left of the garage just at the bottom of the hill. The small size of the available area also means that the owner chose to install a pair of high capacity drywells to absorb septic effluent instead of a more space-hungry conventional drainfield.
Exploratory Digging to Find the Septic Tank
Dig or probe very gently in the area where you think the tank cover is located - SAFETY WARNINGS: beware of collapsing tank covers
and do not work alone - falling in is likely to be fatal - read my Safety Suggestions article above before beginning this work.
What if We Can't Find the Septic Tank?
What if there are no visual clues of tank location and we can't easily find it outside?
If none of the measures described above works to quickly locate the septic tank, the last resort is a bigger digging project which
I describe next.
Cross Trenching: At the building wall where the waste line exits, dig a small trench across the suspected
pipe location going down until you find the pipe. Note its apparent direction.
Move out 3-4 ft. in that direction and dig again.
In other words, follow the pipe by excavating small test trenches across the suspected pipe direction until it leads you to the tank.
This is what an excavator does with a backhoe if they can't find the tank by other means.
Tanks may be distant:
Beware, while the septic tank is often found close to the building (where it's easier to bury the tank and for other technical reasons),
site conditions can make it necessary to locate a tank at quite a distance away.
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Thanks to Donica Ben
who pointed out the danger of digging into buried electrical wires (11/11/07) as we discuss further at Septic & Cesspool Safety Procedures
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