Here's a quick, easy, inexpensive way to seal foods airtight in a plastic-bag. All you need is a zipper-lock bag, and a tub or pot of water.
If using this method for storage, we'd suggest using freezer bags for a better seal. For cooking sous-vide, do not use this method for foods that need to cook longer than a couple of hours. For long cooks, we'd recommend using an actual vacuum sealer. Zipper-lock bags can fail with extended cooking times.