Mastertangler, I don't have any pictures so I'll try to explain.

Tie a bowline in the end of the rope (a trucker's hitch will do, if you prefer), using whatever size rope you choose.  Wrap it around the tree once or twice at about top-of-head level and tie it off somehow.  Friction will hold it in place.  There should be enough rope to hang down a couple of feet.

Tie another bowline in the free end, high enough above the ground so the water bag hangs without touching (gotta keep stuff clean, y'know).

Attach one end of a double snap shackle to the rope you wrapped around the tree.  There will be enough slack in the rope to do this.  The other end of the shackle will hold the dirty water bag.  (I use snap shackles with an open hook on the other end to make hanging the bag easier.)

Attach one end of another double shackle to the bowline you tied in the free end of the rope.  Hang the clean water bag from it, using the bag's nylon web handles.

When the clean bag is full, switch bags; the clean water will now be at a convenient height.

I haven't described the full system, since it includes a 3-gallon reservoir hung from a third hook, using its own hanging rope.  Once you get the hang of the two-hook method, adding a third will be easy and obvious.