:while they may or may not have created the term out of whole cloth, it seems pretty obvious to me (a yank) that it is a reference to PENIS.  "to hose someone" means to screw someone, either in the sexual sense or the defraud sense.  hoser is just an extension of this.  basically a softer version of "fucker", "prick" or "dick"  maybe closer to "wienie" or "dink"? 

 :the other etymologies about gas stations and ice-rinks sound ridiculous.  adolescent frat-boy slang with clear sexual overtones  why look elsewhere?!