Green’s Dictionary of Slang

swim v.

[1980s] (US prison) to conform to prison society.

In phrases

make someone swim for it (v.)

[mid-19C] (UK Und.) to cheat an accomplice out of his share of the proceeds.

swim in golden grease (v.) (also swim in golden lard)

[17C] to be offered and to take an abundance of bribes.