Bladder tanks are fully enclosed shaped bladders used for the storage of liquids and are usually not self supporting. The shape is custom made to fit the surrounding structure. Examples of shaped bladders include: water storage in the keel of yachts, storage to fit into the companionway on large yachts, to fit into shipping containers, under verandahs, under seats and in floor wells of vehicles etc. These bladders often used to store fuel, sewerage, grey water or potable water.