In the days before modern plumbing the Night Soil Man (shit
carter) would pay weekly visits to one's home to collect the sewage receptacle (large metal can) and leave an empty one. This service was usually arranged by the local government authority (the council). As the can was large and heavy the shit
carter would often place the can on his
head, in order to take it back to the shit truck. To make this task more comfortable he would wear a padded hat. The hat would, over a short period of time, become very flat on
top due to the weight of the load.