I was looking at how to transfer water last year. I have Aqua-tainer style jugs, which I do recommend, but they don't have the siphon hose, which I think you are referring to. On Amazon I found several submersible pumps that I think would have fit through the opening on the jugs, when the entire cap was removed.
I didn't end up going that way, so I can't say much more about the pumps than to just suggest you take a look.
I ended up making a shelf to support a jug, laying on its side, and gravity draining into our fill port. I can still lift a 7 gal jug, just don't care to hold it up for a long time while it drains, and that's where the shelf comes in.
The threads for the spout on the Aqua-tainer are garden hose size, which also happens to be 3/4" NPT. I'm sure a creative mind could figure out how to create a siphon hose using a plastic pipe nipple and a piece of hose passing through. So that's another idea for you.