How to tell tenants "Paper Only" in toilet".

[Rick Michaels]

I have a 4 plex that has needed the main first floor drain professionally augered/cleaned out twice in the last 12 months.  It backs up on the first floor out of the drain and through the bottom of the 1st floor toilet. My plumber recommended to tell tenants to only put toilet paper down the toilet & nothing else.   Also, the sinks all have garbage disposals.  What is the best way to explain this to tenants and enforce?