We pay for cleaning the main line each spring, but still have at least once a year a clog that requires calling a plumber.
So far we've paid for it, but I don't know whether this should be the tenant or landlord responsibility.
The clog is usually way down the pipes, further than we can reach with our 30 feet auger.
We've asked our tenants to start using Scott's 'septic safe' toilet paper, and it's improved since, but the clogging has not beed totally eliminated.
We have similar issue in our house, in the same town, but more rarely , maybe once every 2-3 years.
So what would you do? Who's responsible for paying for unclogging? Assuming it's not obvious what has caused it (we had tenants who flushed wipes that were labeled 'flushable'. had to tell them there are no real flushable wipes)