Green’s Dictionary of Slang

pipe v.3

[? SE peep]

1. [mid-19C+] to look over, to inspect.

2. [mid-19C–1900s] orig. of a detective, to follow, to pursue; to spy on.

3. [1900s] to understand, to work out.

In phrases

pipe down (v.)

[mid-19C] (US Und.) to track down and arrest a criminal.

pipe off (v.)

1. [mid-late 19C] to recognize.

2. [mid-19C–1940s] to survey, to assess.

3. [late 19C] to leave, to depart.

4. [late 19C] to dismiss.

5. [1910s–30s] to make jokes.

6. [1920s–40s] to inform, to explain.

7. [1930s] to ‘pump’ a person for information.