Green’s Dictionary of Slang

chug v.2

1. to masturbate [the arm/hand ‘chugs’ up and down].

[UK]I. Welsh Filth 97: The funny feeling in my troosers tells me that a chugging session with Hector the Farmer’s material is well due.
[UK](con. 1980s) I. Welsh Skagboys 125: He’s recollecting the time he caught me chugging Wee Davie off.
[UK]I. Welsh Decent Ride 380: She’s chuggin away, n ah’m half ootside the blinds, keepin shoatie.

2. (US campus) to throw away [var. on SE chuck].

[US]Eble Campus Sl. Nov.