Clifton Sparks gives a late 19th century insight into the D. C. opium trade in a detailed newspaper article (Washington Post, March 8, 1896 p. 14)

As there are different brands of whisky, so there are different brands of opium, and the expert smoker knows them all.

The best brand is known as Li-Yuen. The secret of its manufacture is a closely guarded secret, but it is believed to be a blend of Smyrna and Indian opium. Opium is procured by cutting into the seed vessels of the common white poppy of China, India, and parts of Asia, and collecting the white juice which exudes from the cut. After a few hours this turns black, hardens, and is molded into a lump. It then becomes the ordinary opium of commerce.

The Chinaman takes this and prepares it for smoking by mixing with it a large proportion of water and certain other ingredients, which he prefers to keep a secret. Very frequently it is more or less cooked before it finally gets to this country. It is imported – and smuggled in – in small, square brass canisters, containing from three-quarters of a pound to a pound of the drug. The canisters are never filled owing to the changes which the opium undergoes in travel. If the can were filled the opium would swell and burst the can.

When a Chinaman gets hold of his can of opium he treats it more tenderly than he would his youngest son. It is opened with all due ceremony, and placed in a bowl of warm water to slightly heat it. A sponge wrung out of scalding hot water is placed over the mouth of the can, and a little water is added. By this manipulation the merchant obtains after awhile a semi-liquid black mass of the consistency of thick tar, which is prepared opium. It is then poured into a big, white mug, and vigorously stirred with a stick until is of the same consistency throughout.

Then it is ready either to sell or to smoke. It is a most expensive commodity and to fill the smallest "toi" once, costs a dollar. The raw opium has a peculiar and rather pleasant smell, having the odor of good molasses candy more than anything else.