The back up is usually a result of the actions of the people living in the house, there are certain circumstances(roots, broken drain lines, etc...) that cant be avoided but from my experience, the occupants are usually involved.I've had 3 sewer back ups in the last year and every one was from tenants flushing things down the toilet that are not meant to be flushed. 

I had many problems with them, being loud late at night, trash on the property, and basically had to send a 30 day notice to get them to leave.They actually left the property in pretty good condition aside from some damage to trim around a doorway while moving their couch in, and a ding in the brand new stainless steel fridge.Their security deposit was $875, of which I deducted the following:$30 for one day of rent$60 for fixing the wood trim$100 for the ding to the fridge$258 for a plumbing charge from them using flush able wipes that led to me having the main line snaked out.

For example, let's take a typical toilet problem that involves a sticking flush valve.

I hate to see people flush good money down the toilet. 

Again we paid the bill.At this point we notified both sides that no feminine products of any kind should be flushed. 

The state is flush w $$$$ and probably looking to build homeless shelters that rival the Taj Mahal.And after they are done getting those big, bad, evil businesses, they will go after the SFR.  

I replace toilets with low flow / dual flush models with a high (16.5") height.  

Interesting situation that I am analyzing and could use some ad(vice), questions, discussions to help me flush out the nuances of the two options.

Listen for awhile after the flush.

I don't know if I would put this in the 'Top 5' mistakes, but leaving a weak flushing toliet in a rental property is a really bad idea.