In rail transport, many passenger trains (usually medium and long-distance) have toilet facilities onboard. These are often located at the ends of carriages. Toilets suitable for wheelchair users are larger, and hence trains with such facilities may not have toilets in each carriage.

The traditional method of disposing human waste from trains is merely to deposit the waste onto the tracks. This ranges from the toilets being a hole in the floor of the train, to a full flush system (possibly with sterilisation). This system is still in use in many parts of the world, particularly aboard older rolling stock. The principal drawback is that can be considered crude or unhygenic – it litters railway lines. Also passengers must be discouraged from flushing or using toilets while the train is at a station. Generally the problem is unavoidable, although there are solutions where toilets are automatically locked when the train pulls into a station.

Chemical retention tanks are usually present aboard 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, usually when being attended at a terminal station, or prolonged stop-over. If a train is required in service again within too short a period, the tanks may not get emptied. In this case, toilets may back up and cause displeasure to passengers (the traditional waste disposal methods do not have this problem). Another point of note is that carriages may have less "in service" time if fitted with chemical retention tanks. Apart from the servicing time, system failure is rather catastrophic.