Why are the toilets on the train not allowed to be used when they are stopped, and where do the excr

Because most of the toilets of China's trains are directly connected to the outside world, the sewage excreted by passengers is directly discharged on the rails, if the train approaches the urban area, these sewage will pollute the surrounding environment, and the discharged sewage will disintegrate instantly, and will not cause too much pollution to the environment along the railway, even if there is left, during the time when the train enters the urban area and leaves the urban area, the sewage of the toilet is no longer directly discharged on the rails, but is collected in the toilet, and then processed when the train enters the garage. This not only protects the environment, but also greatly facilitates the passengers.