Most septic tanks are buried so that the top of the septic tank is between 3 feet to 4 feet below ground.
When installing a septic tank you measure the height of the septic tank and then dig the hole at least 3 to 4 feet extra.
Then install the septic tank and bury it.
If you have kids around or plan to you should really bury the septic tank deep enough to allow you to cover the septic tank lid with a concrete block or something so that your child or even someone else's child doesn't try to get curious and open the lid and fall in.
There was a girl who died when she fell into a septic tank at an RV park so bury the septic tank as deep as you can and cover the lid.
Or put a fence around the septic tank where it's located or a boulder that you can move later when you need to have the septic tank pumped out.
Perc tests for a septic tank are good for between 2 and 5 years.
Each health department that does the perc test for your septic system on your land sets their own rules on as to how long the perc test is good for.
But the minimum a perc test is valid for is 2 years but some places the perc tests are good for a period of 5 years then after the perc test time passes and you haven't installed your septic tank you'll need to have another perc test done again.
When you go to your city hall they can let you know how to get a perc test done and they can issue the permits for the septic tank installation.
You can install the septic tank yourself but you must get the perc test done and also have the permit to install it.
The perc test is to test if the soil allows the water to drain out into the soil fast enough and not just sit there and stagnate.