I would add that making the one mark on the tubing may not help that much. The water in the tubing will find its own level on both ends and moving one end also moves the other. So instead of trying to find and chase a particular mark on the tubing or the wall to level from, just have each person make a mark on the walls where the water level is for their end after it has stablized. Then measure up or down from those marks with a tape measure to where you want to do your work.
Basically the same system in using a transit. It doesn't matter how high or low a transit gets set up as long as it is level. Then the appropriate level marks can be made on foundations and batter boards, etc. by calculating the distance from the view in the transit to a particular point with a measuring stick.