Green’s Dictionary of Slang

dub up v.3

[SE dub, to thrust, to poke]

of a man, to ejaculate.

[UK] ‘The Death Of Peg The Mot’ in Frisky Vocalist 14: Each swell, to dub up was his plan, / And of all who kiss’d her, ev’ry man, / Confess’d she did her duty.