Do you think the lines are probably reversed? To me, the line at the back looks like the water-out lines on my FW tank. It has a cover over the end so the fish don't get sucked up in to it. The line at the front looks like it should be adjustable for height, hence, maybe it is supposed to be the line in to the tank, and the siphon out line when the power is off.
But the line at the back is definitely the line in at the moment, because if I pour water into the sump, or if it gets air in it for a second, it's definitely coming out the back line.
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