He asked the sergeant who could give him permission to buy one.

From The Great Mutiny by Christopher Hibbert. Page 157.

Thornhill's brother congratulated them on their safe arrival and told them to dismount as horses were not allowed within the defences. Leaving their horses tied to stakes in the enclosure, they walked towards the great gateway. Passing over a bridge and through a maze of courts, passages, archways and tunnels, they entered at last 'what seemed the courtyard of a castle, but a castle only elsewhere to be seen in dreams or read of in fairy tales'. Lofty walls enclosed it; galleries supported by slender columns ran around it; towers and windows, balconies and small cupolas of white marble loomed above it. Leaving this courtyard through a tall stone arch, they were taken into a long tunnel which led on to a steeply inclined stone ramp that, in turn, took them out on to a large open space surrounded by low buildings of intricately carved stone. Passing through yet another archway, Thornhill entered a garden shaded by trees of the thickest foliage and crossed by paths of shining white stone. In the middle of the garden was a huge marble basin filled with water. Terraces and pavilions of the same brilliant whiteness, topped by gilded cupolas and golden domes, surrounded it on every side. The sun had just risen; the gold shone; the marble glistened. It seemed to Thornhill 'like a scene from the Arabian Nights'. Behind a curtained doorway, his wife and children were waiting to welcome him.

Thornhill soon discovered, however, that conditions in the fort were far less peaceful and comfortable than his first impressions of the beautiful palace had led him to hope. It was excessively crowded, over six thousand people having taken shelter there, soldiers, civilian officials and their families, native servants, half-castes, Italian monks, nuns, Swiss missionaries, American salesmen, even rope-dancers and acrobats from a travelling French circus. Edith Sharpley was sharing a tiny room with three other girls and her mother. There was no window, so permission was obtained to knock a hole in the wall which was discovered to be seven feet thick. Later, Edith's married sister and her baby came to share the room as the cubby-hole where they had been sleeping had been filled with bricks to support the cannon on the roof above. The Thornhills' small room contained not only the families of both brothers and the children's ayahs but also so much furniture that there was scarcely space to move. So, clearing the jumble of boxes and bedsteads from the small room above it, Thornhill decided to occupy that; and, having done so, went in search of water to wash. He found a well, but there was no bucket. Wandering off in search of one, he came upon an English sergeant standing by a cart full of large tin cans such as those supplied to soldiers. He asked the sergeant who could give him permission to buy one. The sergeant did not know, and added with a genial smile that in Thornhill's place he would not waste time finding out. Thornhill took the hint and helped himself to two tins from the cart which, next time he passed it, was quite empty.