Hydrostatics of lifting water up a tube - Sucking vs. Inhaling

Demonstration of two different ways to suck water up a tube. Problem Q1 on Homework 2 in PHYS 252 refers to this demo. Can you figure out the difference between the two methods? I claim that this measures how far underwater I could be and still breath through a tube (i.e., the maximum length of a snorkel) - can you verify this claim? Notice that I only use one of the methods in the U-shaped configuration of the tube. Do you think I could I could make a bigger difference in the two fluid levels on either side of the tube if I used the other method of sucking up water?