Once your sewer line gets tree roots in it, the line needs to be clean on the yearly basis. If you wait until the sewer line plugs up ( Sometimes it could take 2 or 3 years before it plugs up) the roots start getting very large and they are very hard to cut out. If we can get them out, the line will need to be replaced. It can take a couple of hours sometimes to grind the roots out.
It does not matter what size the pipes are for sewer lines or whether it's a gravity fed system or a pressurized system the roots will find their way in.
Here are some pictures from jobs where the roots have gotten into the pipes and septic tank.