Well.. at one of the rentals that is..
T said on Chat last night that she is having main sewer line problems at one of the rentals.. Roto Rooter has been out twice recently to snake the line and keeps pulling out tree roots.. The drains are also slow, and gurgling.. Classic signs of a main line problem (though some will jump to conclusions and blame some of the symptoms on bad venting).
For the fix to this problem, we have to ditch Roto Rooter.. Sure.. They will bid the job, but they will be the most expensive option. Also, each one of their techs is paid commission on each sale, so there is no incentive to cut costs.. You need an independent, one man show plumber that is willing to fix the PROBLEM, not replace a whole main line.. You need this guy:

My bud "John the plumber".. One man show with tools, knowledge and a single van.. he's a service plumber. he doesn't take big jobs.. he likes to do several jobs a day.. if you find a plumber that wants to bid several days for a little problem.. RUN.
After you find the right plumber, you need to have him take a video of the sewer line. he will have a gen eye camera set up similar to this:

This set up will allow you to see exactly what is going on inside the pipe, and also acts as a locator, so you can tell exactly where in the yard the problem is, AND how deep the pipe is. Your plumber should be able to send you a video tape of the problem.. of course, finding someone with a VCR to watch it might be tricky :-) My system is VCR based.. perhaps the newer cameras have DVD recorders.. You should expect to pay around $200 INCLUDING a copy of the "tape" so you can see the problem yourself.
Once you have pictures of the problem, the operation itself is as simple as digging down to the pipe, and replacing ONLY the damaged section.. You made mention of a 4" to 6" section that was perhaps bad.. That could be a joint between an old piece of orangeburg (clay) pipe and newer ABS pipe.. They make rubber connectors for these transitions.
depending on the severity of the problem, and the amount of digging involved,this should only cost between $500 - $750 to repair (Including the camera).
You can save a ton of money if you know a $10/hr laborer that can do the digging.. You don't need a $69/hr plumber doing that!
I will look and see if I can find you a plumber that i like..... Wish you were more LOCAL.. I have all the equipment and the guys to do this.... Pisses me off that you are two states away.