You have two homes in close proximity of one another and wish to put them both on a single septic system. Assuming local building and health codes allow it, this is a straight-forward project.
Determining Size of System
The size septic system needed is based on two factors. You will need the results of the percolation test and the number of bedrooms in the home(s). In this instance, you will need to combine the information from both houses to determine the size system needed.
Run a drain line from each home to the septic tank. Both lines must run downhill to work properly. This may limit your options for placement, but it is unavoidable. The two lines will need to intersect at some point, allowing a single pipe to enter the septic tank itself.
Field lines need to be located in a clear level area with enough open space to accommodate the amount of field line required. How the field line is laid out will depend on the dimensions of your property and the total footage of the line required.
Connecting Tank and Lines
If the tank is situated in such a manner as to allow a gravity flow system, then you need only run a drain pipe from the septic tank to the field line distribution box. If the location will not accommodate a gravity system, you will need to install a pump in the septic tank which will pump the wastewater from the tank to the field lines.
The septic system should be installed in such a manner as to avoid any type of vehicle traffic over the tank or piping system. There should also be no shrubbery or trees allowed to grow over the field lines. The roots from these plants will eventually enter the piping and cause clogs.