Green’s Dictionary of Slang

(US drugs) to remove opium residue from the pipe.

1937		B. Dai Opium Addiction in Chicago 199: Gow it out. To clean out the inside of the bowl of an opium pipe.
1939		Detective Fiction Weekly 18 Mar. 59/1: If you should happen to hear anybody speaking of a suey-pow or a joy-pop or of gowing out the lemon bowl, [...] bring him right here [OED].