A bit of... er... excitement here, coming up, of course on Sunday night, the worst possible time for this sort of thing. Sandy was taking a shower, and the daughter went downstairs to find soapy water coming up out of the washing machine drain line, onto the floor. The line from the house to the septic tank, or possibly the tank itself, was not flowing. Not what one wants to see. The tank itself is pumped out every few years, and as far as I know is working properly, so this must be a thing with the piping. I muscled out the big drain auger, pulled the plug on the cleanout in the "go out" line, and began to auger away. About 15 feet in, the auger just stopped, apparently having run into some immovable something, and no more progress could be made, and no drainage was taking place. This was not a good thing, as we were out of business until at least the next morning. The only option was to add a bit of leftover RV Holding Tank stuff to each toilet in case of emergency, and hang on.
We have an outfit that does the occasional septic tank pump-out, so we called them early the next morning, and they were able to make it out later in the day. They were brave and dedicated etc, and worked in the on-and-off rain, digging up septic tank line from the house to the tank, which is not far, but it still involves digging.
Here is some apparent wisdom, but more likely using whatever there was on hand by a sub-development builder - the drain doings in the house are rather well-done. Outside the house, however, the PVC line from the house to the septic tank changed to about 15 feet of clay pipe, which conducted everything to the tank. Why this was done, I have no clue, but it was part of the problem. Nearby, there used to be a massive hackberry tree, and tree roots had, over the years, displaced the clay pipe sections, causing leakage between the sections. In addition, there was a large watermelon-sized rock on top of the clay pipe, apparently pushed in when the pipe was being buried when it was installed. Over the years, the combination of roots and the rock had damaged the clay pipe, and the pipe apparently just broke up and collapsed, making for the Unclearable Clog.
The plumbing guys worked hard correcting all of this. The roots are no longer a factor, as the tree was taken down some years ago. The watermelon-sized rock now resides in the ravine behind the backyard and good riddance. When the line left the house, it needed to drop about 18" to put it in the right position to do the proper draining into the tank, and was originally done with two 90-degree fittings. Just on the principle of easing the flow, the plumbing guys replaced this little arrangement with two 45-degree fittings to provide less of a sudden direction change, and the house-to-tank line is now a continuous run of schedule 40 PVC, buried without large rocks or other destructive debris. The guys assured me that this part of the system should outlast the house. I'll go with that.
So now, eighteen hours and some several hundred dollars later, everything is in prime flow again. The expenditure puts a strain on the limited reserves, but life is good when toilets flush well, and one can take a shower...