Kathleen, Walking piston: The little yellow tab on the pump connector (new name for the yellow elbow doohicky) needs to fit into the blue slot on the pump. We probably do it automatically when setting up a pump. Moms don't. I often get pumps back with the pistons still attached, but the yellow tab outside the blue slot. These pistons do walk away when running and would need to constantly be pushed in. I now include laminated instruction cards in each pump case. How to put the piston assembly on is instruction #5 for both the Standard and Advanced kits. The laminated cards are from Medela. My Advanced kits and Standard kits seem to generate the same amount of suction when I measure it with a gauge. However, I wonder if, for some reason, the amount of milk expressed and/or stimulation provided is different. The same part fits against the breast.... but...I wonder if this will be like the Classics vs. the Lactinas. Yes, on a gauge they look identical. On the new 'Which Medela Breastpump Is Best For You?" guide, the two pumps are given equal billing. But, in actual use, many of us do see a difference in milk production, comfort and a mother's ability to maintain a milk supply long term. Any comments? I do like the new kits better...but now I'm wondering if I should carry both kits all the time. Elizabeth Novelo Puzar, IBCLC