Alternatively, some parks mandate a pack it in, pack it out rule. Many reports document the use of containers for the removal of excrement, which must be packed in and packed out on Mount Everest. Also known as expedition barrels or bog barrels, the cans are weighed to make sure that groups do not dump them along the way. Toilet tents are erected. There has been an increasing awareness that the mountain needs to be kept clean, for the health of the climbers at least.