1
general::
1. In the lavatory, as in He can't come to the phone; he's in the can. The related on the can means "sitting on the toilet." The noun can is used for both the room and the toilet. [Slang; c. 1900] 2. Completed, as in About a hundred pages of her next book are in the can. This usage originated in filmmaking to describe a completed motion picture, when film was literally put into a can or canister. [Slang; c. 1930] 3. As an out-of-the-money finisher in a horse race, where a horse comes in fourth or worse. For example, He had no luck that day? every bet ended up in the can. [1960s]
American Heritage Idioms