[header] How to make a reusable, inexpensive, and efficient gravity bong [title] Identify the usable socket sizes. [step] They are between ½ " and 5/8 ", or 12 to 15 mm in diameter. [title] Using the mouth of the water/soda bottle, test the fit of the socket. 
[title] Wrap masking tape around the sides of the socket to make a sufficiently airtight seal. [title] Add layers of tape as to ensure a snug fit.