The waistband of my pantyhose keeps rolling down from the waist and forms a "tube around my hips! How do I prevent this?

When pantyhose is too small, it will roll down. From the following site, Exotic Lingerie | Silk Lingerie | Sheer Lingerie and more... -

"A good tip: Before buying, look at the back of the pantyhose packaging to make sure you get the right size. Brands vary with their sizing; the most common is by letters A-C, and plus or queen sizes. Sizing is usually determined by height and weight. If you find that you are on the borderline of the size grid, the larger size is a better choice. When pantyhose is too small, it will tend to roll down your hips at the most inappropriate time, or may rip by just trying to put them on."