One of the first questions is why do you need to know where your septic tank is located.
All single family household dwelling home sewage systems have a septic tank if they do not have a sanitary sewer line or city sewer at their house. Over time because of the usage the tank will need to be serviced, they slowly fill with solids and need to be pumped and cleaned, this you cannot do, you must call septic contractor that pumps out tanks.
If you are trying to locate your tank and do not have a map from when the tank was installed, sometimes the system inspector or county inspector has a map or system lay out. If this fails you should look in the yard for a low spot, high spot, a spot where there is little grass growth or a brown spot, if all this fails the next process will be go inside.
If you cannot find the tank look in the basement or crawl space for an outlet pipe generally a 4” diameter pipe going through the wall to the outside, all house waste lines should connect to this one line, and run out the wall to your septic tank.
Once you locate the line inside, go outside and mark where it goes through the wall and comes outside.
Now look around, if you see no visible evidence where the tank could be, you may want to measure, the tank is usually 10 to 20 or 25 ft. from the house, this is where the tank should be. Next you need to start poking around to find the tank cover, this could be done by using a ½” to 3/4” rod about 4 to 5 ft. long, if you do not have a rod try a pointed bar or small metal pipe.
If the soil is compacted hard you could use a hammer and tap the rod into the ground until you hit the solid tank. If no luck try every couple feet working from the out let pipe, you know where that is, work from the house side back through the tank, this should be a sure thing.
If you cannot find the tank using the probing method you will have to start digging, start hand digging finding the out let pipe as it runs out of the house to the septic tank.
If you give up and cannot locate the tank you should call your sewer contractor they can use a backhoe to locate the tank. This will cost more, but is a sure thing, they will find the tank.
For more information go to: http://www.excavating Info.com