on the rails caused by human waste. They were replaced with bio-vacuum toilets, which use bacteria to decompose human waste, fulfilling a phaseout pledge made in 2010. Chemical holding tank Chemical holding tanks (retention tanks) are usually included on newer carriages and railcars in wealthier and more densely populated parts of the world. One issue is that the tanks need to be regularly emptied, often at a terminal station or prolonged stop-over. If a train needs to be used again quickly, the tanks may not get emptied. In this case, toilets may back up, which can result in toilets being closed. Vacuum toilet Vacuum systems used in the newest carriages are similar to those in airliners: waste is pulled into a holding tank with a high pressure pump. Their disadvantages are the same as of chemical holding tanks, in addition they require stable power supply for working, and flushing of anything else but water and human waste (e.g. toilet paper) can easily break the pump. Composting toilet Some trains may have composting toilet tanks, which use bacterial action to break down solid and liquid waste. Only the broken down clean liquid is released to the trackbed after sterilisation. The solid waste only has to be emptied every half year. This type of toilet is in use in some trains in the Netherlands and Switzerland. Cultural references In the United States, Dvořák's tune "Humoresque Number 7" became the setting for a series of mildly scatological humorous verses, regarding passenger train toilets, beginning: In The Good Soldier Svejk, author Jaroslav Hašek used hypocatastasis to indicate the fruit of hopper toilets, while conveying soldiers' envy and contempt for their general officer: A popular Russian internet running joke and one of the most popular Yandex search requests is "what would happen if you dropped a crowbar into a train toilet at full speed?" Gallery See also Accessible toilet Aircraft lavatory References External links Passenger rail transport Toilets