I've used 1/2 inch clear sight hose to siphon diesel fuel out of combine tank when I needed to change a fitting at the bottom. Bore a hole about 1/4" in the side of the hose, up about 3" from the OUTLET end of the sight hose (or whatever you use for hose). Poke the other end of the hose in the full barrel. Get the other end just inside the empty barrel. Stick an air hose blowgun tip in the small hose you bored in the side of the hose, pointing it toward the empty barrel. Squeeze the blowgun to go. You'll see the fuel coming down the hose and when it gets about to the blowgun, remove the blowgun and poke the hose into the empty barrel. Obviously you have to have the height of the bottom of the full barrel above the top of the empty barrel for any kind of siphon to work.
The blow gun pulls the fuel up the hose on the full barrel end just like if you were sucking on the empty end of the hose. This way you won't have to spit, gag, choke, and barf the fuel out of your mouth. Been there done that. Done this several times. Best not to have to siphon anything, anytime, but when you have to, well, you have to.