I was living in Kazakhstan for a while and had to take the overnight train to Kyrgyzstan for a visa run. They're very old trains. I woke up around 3am and had to use the restroom. The train had just stopped at a station in the middle of nowhere, and it was the middle of winter. I went to the restroom. I flushed. But when I looked down through the toilet, I saw snow and train tracks. These trains didn't have anything to collect waste, they just flushed straight onto the ground. I immediately heard some loud whistles and shouting, and footsteps.
I rushed back to the bed and hoped that no-one saw me, but it was too late, and then we spent the next 30 minutes talking to soldiers. I wasn't sure if they were asking for extra money, or if it was something we needed to pay anyway because we were crossing the border.
It was a tiny train station in the middle of nowhere, and we had no SIM cards, so I started thinking about what we would do if they kicked us off the train. I was actually kind of excited about the idea of building an igloo and sleeping there overnight, and then going to get some help in the morning. That would have been a better story, but in the end they just let us go.
So don't flush any ex-soviet train toilets when you're stopped at a station in Central Asia.