Bangladesh has the highest population density in the world. Half the population don't have any kind of toilet, so they have to go outside wherever they can. Spread around by livestock and people, faeces ends up contaminating homes and food. The resulting diarrhoeal diseases, according to Water Aid, kill 125,000 children under the age of 5, every year. In the International Year of Sanitation, Earth Report travels to Bangladesh to discover changing attitudes to hygiene.