Only use Gatorade or G2 bottles for the sensory bottles they are a heavier plastic so they hold up better and keep a unison look so everything looks good. They come in different sizes you can find smaller ones for small hands if you need to.
Make sure to ALWAYS seal your bottles securely! I cannot emphasize this enough. Unless you want your bottle opened and the contents poured out. SEAL IT… with glue. Duct tape can be peeled off by a determined kiddo. Glue is much harder for them to open up.
Use Tornado attachment found at Teacher Stores to create tornado in a bottle. These generally have to be made with two 2 liter bottles or with bottles that have the same size spout. I prefer to find smaller size bottles with similar spout sizes. The twist I am referring to actually comes from Steve Spangler. If you add a small amount of lamp oil to your tornado bottle it highlights the tornado! Less is more here, if you add to much lamp oil it makes it so that your tornado does not function properly. So just add a small amount. You can play with it to see the right amount for your bottle.
**Make sure you seal your bottle very well lamp oil is extremely harmful if swallowed***
For a list of ALL my amazing DISCOVERY BOTTLE IDEAS click the link or the image below