Why is it called a blow job?

Q: I would like to know why it is that they call it a blow job when in reality, you actually suck? I am very curious about how it came to be called the blow job as opposed to the suck job. Please help me out with this.

A: You ask a fine question. It seems that there are several competing theories for the origin of this phrase. The two most convincing explanations we found were the following:

From Ask the Couch:

“This term, now widespread in English-speaking countries, spread from the USA in the 1960s. A puzzling misnomer to many, to blow in this context is probably a euphemism for ejaculate, a usage occasionally recorded in the 1950s. This may itself be influenced by the there she blows of whaling cliche. An alternative and equally plausible derivation of blow job is from the black jazz musicians hip talk expression blow meaning play (an instrument). This term probably caught on in Britain and Australia simply because there was no well-known alternative in existence.(1)”

…and…

From the Maven’s Word of the Day:

“This question has been asked by absolutely everyone I know. And for all the wondering we’ve done about why anyone would give the act of fellatio such a misleading sobriquet, there has been little written about it. There are, however, two well-argued schools of thought.

One explanation ties the phrase to the jazz slang blow meaning ‘to play an instrument’. From there you get the semantic connection of working a tool with some skill, presumably involving the mouth, and there you go.

The second school of thought proposes that the blow in blow job indicates the climax, and is also related to the expression “to blow off steam.” Although the phrase blow job dates only from the 1940s, there is a reference to blowing (someone) off, roughly equivalent to the modern phrase “getting (someone) off,” in David W. Maurer’s 1939 glossary, Prostitutes and Criminal Argots.”

There are many other competing folk etymologies for this phrase, but these at least seemed to ring true to us.