We used to make so many bongs when we were kids.
We went to a local plastics store where you could buy lengths of the plastic tubing to make a bong.
Get a Length of tubing, glue, 1/4" drill bit , grommet and a piece of plastic for a base.
Glue base on.
Pick a spot on the tube where you will drill the hole for the bowl. take into account how you will light it for positioning.
Heat up the spot with a lighter and then push onthe softened plastic with the end of a broomstick/dowel
This would make the indented spot you drill the downstem hole in
use a 1/4" drill bit to make the hole for your downstem.
Put a grommet in the hole and add downstem
sand the mouthpiece end smooth or add a plastic mouthpiece from a diff bong
We had so many plastic creations.