The idea is to unscrew the fill fitting from the tube (after being very very sure it's empty of course), it should not be very tight. You can use the barrel band as a wrench by loosening the two set screws and pulling it off then putting it back on upside down (so it doens't go around the barrel), tighten the screws again before using it for leverage to get things going.
Then you insert the unit into the tube. Guys have used all sorts of stuff, the basic idea is to loosely block the tube (has a hole in it) somewhere near the middle with something that doesn't move. It kills the 'echo' in the tube as the air is let out.
Hopefully someone who's done it can provide exact details on how they did it (not that I think there might be many ways to skin this cat....), but that's the idea and where it goes.
Doug Owen
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