I traveled around China in 1986, back when everyone was still wearing blue Mao suits and riding bicycles - so not exactly modern China. Several train trips mixed in with a few buses, planes, and day trips by taxi.
One was 2 1/2 days from Beijing to Urumqi, capital of Xingjiang Province Central Asia. The tickets to choose from were hard seat, soft seat, hard sleeper and soft sleeper. We got soft sleeper, which was a set of bunk beds on either side of a private room. The other couple in our ''room'' was some Chinese military officer and his wife - full uniform, all the ribbons and medals, etc - and they were not at all happy to be bunking with a foreigner. They didn't say a word the whole time, probably thought we were spies or something, and nervous to even be near us.
The rest of the train was mostly Uighurs going back home. At some point I realized I wasn't at much of a disadvantage, hardly any of the other passengers read or spoke Chinese either.
The train more or less followed the northern route of the old Silk Road, and we could see parts of the Great Wall off in the distance. After the first day most of the rest was through the Gobi desert. Omg the train stopped seemingly constantly, at every little village. Most of the stops weren't even villages, just train platforms in the true middle of nowhere. The food on the train was crappy, and all the little stops were only for a few minutes each, so no getting off. When the train stopped, the peddlers on the platform (there must have been villages or small towns somewhere around) would surge forward and sell bread, fruit, and whole cooked chickens through the train windows.
The train had a bathroom car. An empty, unlit, windowless metal box, with no railings, stalls, anything, just a hole in the floor in the middle of it. The bathroom car was locked about 15 minutes before we came to the next stop, and 15 minutes after the train left town. I guess because everything from the hole in the floor just dropped to the tracks.