Wiktionary

1. tonk(Noun)

   Term used, primarily by US immigration officials in informal settings, to describe an illegal immigrant of any country.

2. tonk(Noun)

   An item of value, or of perceived value, especially for sale

   How much tonk have we got to shift? etym. uncertain.

Origin: Origins are unknown, but definitely predate the use of metal flashlights, contrary to the most quoted description of origin.