Green’s Dictionary of Slang

(US prison) to confess, to turn State’s evidence.

1931		G. Milburn ‘Convicts’ Jargon’ in AS VI:6 438: do a solo. To turn State’s evidence; to make a confession to the police.
1949		Monteleone Criminal Sl. (rev. edn).
1950		Goldin et al. DAUL 59/2: Do a solo. To confess a crime, implicating one’s accomplices.

to fellate.

1975		‘Ray Strong’ Naughty Niece n.p.: 'On his superb skin flute she could play a masterful solo, feeling his pre-cum drip out quickly or slowly, depending on how her lips applied themselves .
c.1980		B.F. Dickens When She Was Bad n.p.: [H]er tal¬ented lips and tongue played an erotic solo on his meat flute.
1990		B. Elton Inconceivable 60: [I]t being as much as three or even four days since I last played a solo on the one-stringed bass.
2000		Cum Junkies 1 🌐 He munches on her as she's laying back on the couch, before offering her his meat whistle to play a solo on.