I build horns!!!!!!!!!!Water/air tight......................... After you install the butt plug,,,I roll up balls of bees wax,feed them down the spout,,,now take a hair dryer,so borrow one,,tilt the horn spout up,butt down, and heat the horn around the butt plug with the hair dryer,now put your lips on the spout and GENTLE blow,pressurize the horn,, roll the horn around and around.The warm/melted bees wax will fill any/all voids and then let the horn cool.The horn is as water tight as a ducks butt.
Been doing it this way for 30+ years,,NEVER had one leak,,NEVER....N E V E R