The up an down motion they detail isbecause of a check valve they have in the line I believe. On the downward shove, water will go up as the tube is shoved in to the water. As you pull back, the valve should shut and trap the water. A lot of work that just agitates the whole tank.
When I use my python, without the sink faucet venturi, I pick a spot about 2-2 1/2 feet down from the vac tube, pinch it off with a double fold of the tube. I take the vac tube, and with the end that is connected to the hose, push it down into the water, open end of vac tube up, and when it is below the surface, it fills with water. Then I raise the vac tube up high, and water flows down to the pinch point. Then I put the vac tube back in, same as before, let it fill, then point the open end down onto the gravel, then release the pinch point and you have flow.
If I was going to a bucket,, I would just start it with a suck on the tube, but my 75 foot hose is used to drain the tanks outside.