Hi @Traci150
We grew up with Septic Tank systems and have friends who work for Council and part of their role is with wastewater.
Did you try claim the damage back through Insurance?
Those broken pipes are a jolly nuisance at the best of times.
It's unfortunate your Guests didn't advise you during their stay, however there may be a genuine reason for not doing so, including not knowing where it was coming from.
When living in rural areas one needs to check water lines regularly.
All the best from Auckland, New Zealand