Thanks for the update - that's interesting. It sounds like you know what you're talking about. If the pump does indeed throttle down, then you're right, teeing off just wastes energy. I'd be curious to know what pumps throttle down: all pumps, good pumps, powerheads...? Also, I realized that all of us have been saying "back pressure," but isn't backpressure when the intake of the pump is restricted as opposed to head pressure which is at the output?