Why does water eventually stop moving up the pipette?Can the observations be explained in terms of tonicity alone (using the terms hypotonic, hypertonic, isotonic)?

Water moves into the dialysis tubing "sausage" down a water potential gradient. Since the "sausage" is open-ended (connected to a pipette) water flow into the "sausage" results in fluid flowing up the pipette. Water will flow into the "sausage" until the pressure exerted by the column of fluid plus the osmotic potential of the fluid is equal to the water potential of the distilled water in the beaker. The observations cannot be explained in terms of tonicity alone (pressure is also a factor in this case).

If you had two solutions, one that was 30% sucrose and the other 60% sucrose, which solution would have the more negative osmotic potential?

The greater the solute concentration, the lower (more negative) the osmotic potential of a solution. In this exercise, the 60% sucrose is more concentrated than the 30% sucrose solution and therefore, has a more negative osmotic potential.