What is a "Water Lifter" ?
This is the way the lock is filled and emptied!

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This is how you can empty a fish tank:

Put in a hose, let it hang down outside, suck the other end the hose with your mouth until the water is coming. Now let the water
run freely. Or fill the hose with water and put a finger tightly
over each end. Put one end under the water in the tank, and the
other end at a lower level outside, and remove your fingers
from the ends.

 

This water column has an additional 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, so that this additional water column builds up.

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The trick with the Water Lifter:

  It doesn't run.
The Lifter is still filled with air.
 
 
 
 
 
 
 
 
 

 
 
 
 
 
 
 
 

The Lifter is evacuated. The pressure difference pushes water into the tube.

  Now it runs!