Incredibly it all happened a couple of minutes' drive from numerous public toilets. There was no reason for the bus to make a toilet stop there, on State Highway One, in full view of passing traffic and living room windows.
I'm not some evangelical prude. Growing up as a keen hiker there were times when you were a long way from the nearest convenience. But that old motto always applied, leave nothing but footprints, take nothing but photos.
That wasn't the case here. Toilet paper and other waste was left behind.
After being notified on Friday evening I got in touch with the bus company. They're yet to answer my questions about how they'll ensure this doesn't happen again, but I understand that an independent tour operator had hired the bus.
It's important they take what happened on Friday seriously. This shouldn't happen in Tinwald, or in any part of our country.
The fact that it does was apparent to us when Parliament sat last week. On the agenda, a draft piece of legislation to increase the maximum fine for incidents like this, and other littering, from $400 to $1000.
The sponsor of the legislation, the MP for Coromandel, highlighted examples in his own community of what happened in Tinwald.
At the Select Committee prior to the vote, all Councils who submitted on the legislation were in favour of it, except Auckland.
The Ashburton District Council strongly supported the legislation, noting that the current maximum fine is far too low. I agree. If we are to ensure a proper disincentive to the sort of behaviour we saw on Friday, the maximum fines should be increased substantially.
There are other avenues that can be explored in this case. I understand that the bus company has made a complaint to Police. I also accept the infringement process open to councils has flaws around the level of evidence required (the concern expressed by Auckland Council). They could have easily been worked through by amending the legislation as it progressed through Parliament.
Unfortunately we won't have that opportunity. Despite the near-unanimous disgust in our community at what happened in Tinwald on Friday, and has happened in other parts of New Zealand, the Labour Party voted against the legislation, which means it won't progress any further.
That's a shame. Without tough disincentives and stronger tools from Parliament, I'm worried these shocking one-off occurrences will only become more regular.
Andrew Falloon is the MP for Rangitata