Upon retiring we moved a new home in NC with septic system in 1993. One of the upstairs toilets backed up occasionally, always when we had visitors! (Appx 12 times total.)Later the downstairs toilet adopted the same pattern. The other upstairs toilet has now started to follow the pattern.( Remember this is over the coures of 14 yearsFrankly We have spent enough restoring ceilings and repainting to install new plumbing but no one has convinced us that they properly diagnosed or can fix the problem.

Over the years we have called several local plummers and finally Roto-Rooter. They have each said the system is clear and they try to sell me new commodes as the solution. As this was first just one, three new johns didn't sound correct. My thinking (I am not qualified to think much less plumb) is that a blockage of some type must be in the line after they join before entering the septic tank. The 1200 gal. tank has been pumped every 5 years. In fact pumped last week after the latest back up.

Does this type system have a clean out or back flow valve. Would a video be worthwhile.

I very much admire the quality answers I have read on this site and would sincerely appreciate any advice as to what to look for, questions to ask plummers etc.and of course a solution would be dynamite!

My guess: Since you have a septic system you probably have well water. There is a possibility that the holes under the rim of the toilet are calcified. It's tough to clean them effectively (coathanger one at a time).

When you said you repaired ceilings, can I assume that is because the toilet backed up? If so, then I would suspect the toilet flange. When the toilet overflows, the water from the toilet goes under the toilet and onto the floor below. If the seal is good, that won't happen.

PS: Toilets with the Flushmate system (pressure assist) seem to be able to flush anything.

PPS: If you replace one toilet and the problem goes away then you know what the problem is. You might want to consider whole house water treatment as well.