Section 141(viii) in Police Regulations, Calcutta, 1968
(viii)Prisoners shall be taken out to relieve nature at as late an hour as possible before Officers retire to rest, in order that it may not be necessary to open the lock-up during the night. Before being taken out they shall be secured with leg shackles, handcuffs or rope. When relieving nature they shall be attached by means of a rope to a constable.
