With hot glue, glue one soda bottle cap to the bottom of the bottle. Nothing sticks to PET, so you have to put hot glue "rivets", just let the hot glue go through the holes and then glue the soda bottle cap.
Put the threaded tube into the bottle through the bottom hole. Place the second soda bottle cap at the other end and screw it to the bottle neck.
Pass through the hole of the elliptical base the threaded tube and screw the hex nut to the threaded tube.