@Sarah977 Yeah, the toilet was working just fine when we arrive.
I am not an expert with how a toilet works, but from my past experience, I do know that the clogging of a sewer drain could be a build up process. And I Googled a little bit, and found out the reason we could throw toilet paper into the toilet is that toilet paper will take time to dissolve in the paper, which by itself, takes time.
We have a few hypothesis:
H1. this is a build-up process, but we are the one who nailed the coffin.
H2. we have a large group of people sharing a single one toilet. In other words, we are overloading the toilet, and the toilet paper does not have enough time to dissolve. eventually led to the clogging.
H3. one of us throw too much toilet paper into the toilet.
I think we should not be responsible for this if H1 or H2 is the root-cause. But the overall point of argument here is that no one really knows what happened, and eventually, we were made to pay for this bill.