2 liter bottle to 2 liter bottle adapter cap

thingiverse

My son wanted to create a tornado in a bottle experiment, so we decided to attach two 2-liter bottles together. This way, the soapy water tornado could drain into the opposing bottle efficiently. To make this happen, I created an adapter that threads onto the bottles where the bottle cap goes. The threads on the adapter perfectly match those on the bottle, ensuring a secure connection. The bottle adapter is remarkably thick and strong, making it almost completely leak-proof. However, there was some minor leaking when we assembled ours, so I used tape to ensure a good seal. I printed this design at 102% size, but it should work just as well at its original size. If you find that the print is too tight a fit and won't properly thread onto the bottle, try sizing it up slightly to 102%. This will give you a snugger connection. To set up the experiment, fill one bottle to the top with water and add a short squeeze of dish soap for better visibility. One drop of light-colored food coloring will also help improve the view. Next, thread the adapter onto the full bottle until it's snug. Then, thread the empty bottle onto the opposite end of the adapter until it's snug as well. If you notice any leakage during assembly, simply wrap the joint several times with electrical tape (as shown in the image).