2 liter bottle to 2 liter bottle adapter cap

thingiverse

My son wanted to make a tornado in a bottle experiment. We found the best method would be to attach two 2-liter bottles together so the soapy water tornado could drain into the opposing bottle. I made an adapter that threads onto the bottles where the bottle cap goes. It's threaded to perfectly match the threads on the bottle. The bottle adapter is very thick and strong and it's almost completely leak proof. There was very minor leaking when we assembled ours so I used some tape to ensure a good seal. I printed this at 102% size but it should work at its original size. If you print this and find that it's too tight a fit and won't properly thread onto the bottle, try sizing it up slightly to 102%. Fill one bottle to the top with water and add a short squeeze of dish soap. For better visibility, add one drop of a light colored food coloring. thread the adapter onto the full bottle until snug. Thread the empty bottle to the opposite end of the adapter until snug. If there is any leakage, wrap the joint several times with electrical tape (see image).