In theory you can put a glass or acrylic viewing window in any container, tub, tank, box etc etc. It's how you attach it that's the critical part. Firstly due to the flat rigidity of the viewing panel it helps considerably if the area where the panel is going is also very flat. So curved containers, even slightly curved, would cause you grief.
Glass is brilliant with silicone, acrylic isn't. Then it will depend on what the material of the "container" is made from, and whether that is good with silicone or not. If both panel and container are compatible with the bonding agent, then it's easy. If not you have to go down the route of drilling the viewing panel (acrylic is easier if this is the case) and attaching it to the container with nuts and bolts, with a layer of bonding agent in between to act as a gasket/seal.