There is absolutely fluid in the pipes - this is the principle behind heat pipes, HOWEVER, there are a few different designs. I deep dove the physics on the designs of heat pipe systems in order to better understand the issue.
http://www.electronics-cooling.com/1996/09/heat-pipes-for-electronics-cooling-applications/
This link is GREAT! So, it comes down to this. VERT vs HORZ is inconsequential IF the heat pipe design is such that it incorporates a "wicking" liner in the heat pipes. The capillary effect SHOULD be such that it is capable of overcoming gravitational effect on the mass of the fluid itself. And since this is the case with water in soil in nature, it would stand to reason that VERT vs. HORIZ should not matter provided that there is wicking material in the hyper 212+ design.
There are 3 different orientations strictly as an FYI... Vertical, Horizontal, Vertical (inverted). In theory, all 3 should perform the same if the capillary action works properly.
Back to the original question about orientation... I would say that you want to "push" air with your FIRST fan through the condensing area or fins of the device (there's no limit to increasing pressure, but there is a limit to drawing a vacuum). A second fan would be just the opposite; it should blow away from the fans or draw a vacuum on them increasing the throughput of the fluid (air) flow. In other words, the 2 fans should both be blowing in the same direction.
The flow direction of the cooling device (1 or 2 fans) SHOULD match the MAJOR flow of air through your case. Generally speaking if your largest and most numerous fans run air from front to back through your case (true in my case), then point the unit toward the back of the case. If you have EQUAL air flow front to back, and bottom to top, I would point your cooler toward the TOP of the case so as to take advantage of the natural convection current in the case -- this assumes that the airflow can leave the top of the case. If you are blowing the air to the top of your case only to allow it to sit there and get blow out the back, pointing it up doesn't make sense. The other thing to consider is... are there MAJOR obstructions between the flow of the CPU cooler and the case fan that would expel the air from the case? If so, this will just create turbulence in the case and reduce (or at least, not increase) the total throughput.