For real though, this is a cool idea and hack, but only a real bastard would put the toilet out of action deliberately. Of course that sort of person does happen to frequent British trains and this is hence valuable research.During the Polish train hacking debacle it was suggested that saboteurs be charged with harming vital national infrastructure, I hope that toiletblockers would be similarly indicted.
Here in Germany, the railway itself is the worst culprit - in December, when DB took over the notorious Hof-Munich line, I travelled on a 6-car double decker train that had 5 broken toilets, all of them because either the water was out or the sewage tank full. Not fun.
The second worst culprits are idiots throwing trash into the toilet. Diapers, tampons and wet wipes don't belong into regular toilets - but especially not into vacuum toilets like on trains or planes.
Czech trains on the other hand? They run actual restaurants with legit chefs on board [1][2].
[1] https://ostkoster.de/speisewagen-und-mitropa-in-ostdeutschla...
[2] https://www.tagesspiegel.de/gesellschaft/im-knodelexpress-ge...
It's not a free ride, your nephew is just dishonest.
It's not particularly admirable behavior, but it's not all that different in kind from using a whistle from a cereal box to make free phone calls.
The one you describe is the more famous one, but there was another one a few months earlier, where a group of actually malicious hackers used simple radio signals to trigger emergency stops on dozens of trains over the course of a few days.[1]
[1] https://www.wired.com/story/poland-train-radio-stop-attack/