I use the standard 5 gallon cans and put them on a shelf above the height of my Duc. I then use a super siphon like here:
http://www.xtend-a-hitchnorthwest.com/super_siphon.htm to transfer to the bike. A few shakes and it is going and then just lift the siphon head out of the gas to stop it. It is really easy and I have yet to spill a drop since. Just straighten the hose out to drain it into the bike after taking it out of the gas can. I don't remember where I got mine as I have had it for many years. I just linked to what came-up on a google search.