Unknown tenant causing plumbing issues

[Aaron W.]

In one of our fourplexes, we a tenant (or tenants) who are flushing wipes, paper towels, and other unknown objects down the toilet which is causing plumbing issues. Our property manager has called the plumber out to the complex multiple times this past month which is costing us a little over $300 each trip. The property manager and plumber have been unable to identify which tenant (or tenants) are doing this so they advised all of them about this issue and to not flush anything other than toilet paper down the toilet. 

If this issues continues, what have you done to try to mitigate this issue?  One thought it to charge all the tenants for the plumbing charges.

TIA