It is never good to be cleaning the sewer for your house (probably a 4" line) using a small gauge cable through a tiny access. I wont touch a plugged sewer line unless I can get my 3/4" or 11/16" cable down there. This way I can also get the larger root cutting head into the line and clean the pipe better. I don't know why your pipe backs up every couple of years, there are plenty of possible reasons. Roots are very common, or the line could be damaged or installed incorrectly. It would be hard to say without more information. Some of my customers need the roots cut out of the sewer line every year, some get by with a cleaning every 30 years. It may be cheaper to spend a few hundred bucks every year for a cleaning rather that spending thousands on a new sewer line. In your instance I would look for better access to the sewer line too clean it with a bigger cable. If you do not have an accessible clean out cap in your basement or crawlspace then things can get tricky. You can pull the toilet off of the base, provided you dont have a soft lead closet bend. You can go down through a 4" vent stack on the roof, provided you can work safely from it or you get out your shovel and dig it up. Many heavy equiptment rental shops rent large sewer snakes. Be careful with these machines though they can be tempermental. Just ask the master plumber at my shop, old Boyd, how he lost his thumb in a sewer snake.