I am not sure if the manual has been changed since I purchased mine in '13, but mine shows pulling from the top and returning to the bottom. This is how I hooked it up, as well as everything else such as grounding rod, thermostatic bypass etc. Went by their manual so if/when I have an issue and may require warranty repair there should not be a problem.
Anyways mine has been excellent so far except I had to replace several grate bricks after only the second season. The original ones were an issue with moving around if you raked your ashes to much or tried to reposition a large chunk of wood and the gaps would open up on some and close somewhere else. I installed the new style brick with the built in spacers.
I have only added water once this season, a total of 2 1/2 gallons, but it is due again soon but will wait till it is shut down for the summer and after I have sent in my water sample and received my results.