torin3, you are absolutely correct. However, the 10m maximum height for a siphon applicable only as a differential in pressures caused by the ability for water to freely move.
If you have 20 meters of rise above the pump (ridiculous for a contained unit, but not ridiculous for a system like Bladerunner's where he has the PC hooked up to a reservoir in the ground), you won't get a vacuum. If the system is open to atmospheric pressure, you would not "see" the force (imparted by the pump on the outlet) at the inlet side. If it is closed, the head that the pump produces is lost in 1) friction and 2) pressure differentials allowed by air bubbles and flexible tubing.
If this wasn't correct, we'd have a terrible time getting water delivered to our houses, and systems like a hot-water recirculating pump wouldn't work.
edit: after reading Jaydee's post, it seems I am just restating what he said but in longer and windier terms. Ooops!
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