This water column has an
weight, that drags down and "pulls" at the water in the hose.
(Caution: BAD PHYSICS ! Better: The air pressure presses the water into the hose on both sides. The pressure at the lower end of the hose outside the fish tank is of the same value as the pressure on the water surface in the tank. But the additional water column between water surface and the lower end of the hose builds up a hydrostatic pressure that has to be subtracted from the air pressure on this side. So the overall difference in pressure makes the water flow).
It is important to have the hose filled with water,
that this additional water column builds up.
The Lifter is evacuated. The pressure difference pushes water into the tube.