@Kaye36
Not a lot you can do in terms of compensation - as a host you are expected to check your property over once a guest has left and not leave it for a few days. If you can't do it then someone else should on your behalf. I also find it strange that you just didn't call out an emergency plumber on the Monday - I would have done that so as not to lose an 8 day reservation.
You would also have to prove that the guest did something wrong to break the flushing mechanism. Flushing mechanisms break over time - and again, AirBnB would expect you to have contacts and suppliers in place to do an emergency repair.
That's not of much help to you I'm afraid - you could give the guest a bad review, but to be honest if I was the guest I would be in touch with AirBnB to remove it as you could not prove how the damage arose- wear and tear, acccidental damage or deliberate damage.
Good luck