GUANGZHOU－Janitor Huang Xueying has nine cleaning rags, two different colored mops, and several bottles of detergent, among other custodial supplies. "Colors are used to distinguish tools used for different purposes," he said. "The blue rag is for toilet seats, and the white for mirrors."

Huang, 43, works on the G79 high-speed train between Beijing and the southern city of Guangzhou, Guangdong province. The train is among thousands running during the Spring Festival travel rush, which began on Feb 1.

Around 390 million passenger trips are expected to be made during the 40 day travel frenzy, up by 8.8 percent compared with last year.

On older trains, often overloaded during the rush, lavatories used to be a nightmare. They were often left with muddy floors, dirty squat toilets and wastepaper littered everywhere.

The situation has changed as China has upgraded most of its trains. Newer bullet trains are equipped with vacuum flush toilets and staffed with full-time cleaners, such as Huang.

On the eight-hour trip, Huang must check on sanitary conditions, execute a thorough cleaning and make notations on eight toilets in four carriages every 30 minutes.

"I take more than 22,000 steps every workday," Huang said.

Boxes of air fresheners and disposable toilet seat covers are available in every restroom, as are sinks and huge mirrors. There are also single-use combs, liquid soap, hand cream and plants. Toilets with disabled access and babycare facilities are also available on some trains.

"Everything is sterilized. We want to provide a clean and comfortable toilet environment to make passengers feel at home," said Zhong Zhaoshuang, chief conductor of the G79 train.

More modern vacuum toilets have replaced the former squat varieties, which were simply holes in the floor allowing waste to fall directly on the tracks below, said Zeng Guangxiang, a senior railway officer.

Almost all high-speed trains now have 16 vacuum flush toilets, allowing waste to be collected and then treated at certain stations.

According to Zeng, the change has significantly improved sanitary conditions along the route, lowering the concentration of flies and mosquitoes, and effectively preventing the spread of some diseases.

The improvements on trains are part of the broader "toilet revolution". In 2015, the China National Tourism Administration began a three-year project to build 33,000 extra toilets and upgrade 24,000 existing restrooms in scenic areas nationwide to provide clean, free and well-managed public facilities.

"Clean and odor-free, the toilets on G79 are some of the best I've ever used on a train," said Lan Zhengqiang, a 64-year-old passenger. "Sanitary conditions have greatly improved in Chinese train toilets."

Such feedback is music to Huang's ears. "It's backbreaking work, but serving passengers is our duty," the janitor said. "As long as they are satisfied, it's all worth it."

Xinhua