there was a shop I used to work in years ago...this woman used to pop in every day to have a friendly chat with the manager...before she left she'd say "im just gonna borrow ur loo" (every day people) and would leave a massive shit in it. how she didn't know she left it is beyond me...and they would never flush!!!!!!!!!!
The trick to getting a poo down that won't flush (at least i learned one thing from that job) is to get a large volume of water (the toilet bin/bucket worth) flush the loo and poor the water in from up high at the same time. the offending turd will be jettisoned down the u bend forever...