Green’s Dictionary of Slang

backslang it v.

[? link to back slum under back adj.2 ; the term predates the linguistic variety of backslang, while there seems to be no link to slang n.1 itself; ? link to sling one’s hook v. (1)]

1. [early 19C] to make a deliberate detour to avoid meeting a certain person or persons.

2. [early 19C–1900s] to leave by the back door, thus to leave surreptitiously, quietly.

3. [late 19C] (Aus.) to request lodgings from strangers as one travels through the back country.