If your existing septic tank is performing well and is well below its maximum capacity for usage, it is possible to add additional input lines to the system. In order to accomplish this you will need to tie in the new addition to the existing system without disrupting or altering the existing system in any manner. The location of the new addition and the method of installation used for your current system will have a great deal to do with how difficult this task will be.
Locate the drain line running from the current home to the septic tank. This can be done by finding the main drain line under your home and marking where it travels beneath or through the foundation. Outside the home, move along this line until you are approximately eight feet from the home. Dig down until you locate the drain line. The line should be buried no more than 24 inches below the surface and should be a 4-inch pipe.
Once you locate the drainpipe, continue digging until you have exposed approximately three feet of the pipe. You will also need to dig down slightly to allow access all the way around the pipe. From this point dig a ditch to the start point of the new field line. This ditch should be on a direct line and be on a slight incline from the existing drain to the start point of the new drain. Remove all large rocks and roots from this ditch.
Lay sections of four-inch PVC pipe from the new drain point to the existing drain line. Be certain to use PVC pipe cleaner on all pipe ends and fittings before applying PVC cement. Connect the drain line to the new drain point, making certain all fittings are secure. Make certain there are no appliances in operation inside the home, then use the hacksaw to cut into the existing drain pipe. Make two cuts approximately six inches apart. Clean both ends of the opening completely, removing all burrs and small pieces of pipe.
Insert the tee fitting into the opening you have just created. You will need to flex the drainpipe and wedge the fitting into place because it will be a very snug fit. Clean the fitting and pipe ends before installing. Once you apply the cement, you will need to work quickly to get the fitting in place because the cement will set very quickly. Adjust the fitting so the new inlet is directly in line with the new pipe. Measure and cut a section of pipe to fit between the tee fitting and the new drain line. Make certain all fittings are secure, then back-fill the all ditches. The system is now ready to use.