Tenants of going on three years. Excellent overall, pay early or on time. Never an issue. Recently tenant contacted me, pipe backed up, sewage into house, damaging original wood floors beyond repair.  Tenant said he was trying to fish around in pipe also, and found another toy. 

My house is historic and terra cotta pipe still in places. So used home warranty, part of line broken underneath. Had to jackhammer into foundation, dig down repair Terran Cotta pipe, put back together. Nightmare and probably very inconvenient for tenants and baby. 

While fix underway plumber also stated blockage was caused by a kids ball in the line. Now before tenants moved in the house was winterized and vacant for three years. I had a management co and right before moving in my then manager flushed the lines. and there was no problem until now, two years later. 

Now another part of pipe also "sunken" under kitchen area, and flooded, camera wont pass. or see beyond foundation of house. 

First invoice total for me is $2480.00 then second invoice hasn't been executed yet, for sunken area, so not known if further tenants kids items might be in there or not.

Question is: The reality is they are excellent tenants and i don't want to burn any "relationship".  But i also don't want to have them think they can mess with my plumbing and i will just take care of it. 

also this is a single family standalone home, both tenants work and they have two small kids, one is an infant. 

I know they should be paying for the first repair where is definite they caused it. 

Should i be sending an invoice for half for most of the repair? or how would you assign a dollar value to the cause of the issue vs the cost of accessing the issue and then re-cementing, etc?

Also, should i be waiting for the second repair for sunken pipes to be done then send invoice. 

Any advice appreciated! :-)

Thanks!