Ok, the problem is that flow will drop with pressure in a water system just like it will in any system. The problem is that these pumps are designed for high flow and low pressure so the drop is pretty quick, in some cases even the best pumps are only pushing ~50GPH real world after you figure in the water blocks, tubing and radiators. This is one place where the Eheim's excell, they don't drop off like the other and are able to push more pressure before stalling out.
For the tubing, most people use standard worm screw type hose clamps...they are cheap, available and they work but aren't very pretty. For me, I will be doing all my tubing in braided stainless with AN fittings, just for looks really but it is a bunch more expensive (I just happen to have a bunch left over from the fuel system in my Mustang
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