A toilet is a sanitation fixture used for the storing or disposal of human urine and feces. In developed countries, different forms of porcelain flush toilets are common: seats are usually used in the West while squat toilets are common in East Asia. These are connected to a sewer system in most urban areas and to septic tanks in less built-up areas. In many developing countries, dry toilets such as pit latrines and composting toilets remain common. These require little or no water, with the excreta being removed manually or composted in situ. Chemical toilets are also used in various contexts, such as passenger trains and airplanes.