I made up a diagram on how the choke works. It's a cut-out view from the side, there are springs on the left that keep pressure on the mechanism keeping the rightside flush with the main part.

It's like a reverse choke, you press on it to open it. Hit hole, choke, shotgun... all the same. It works beautifully... get's nice think smoke inside then press the choke and wham! it's all in your lungs my friend.

Yeah, a bong has to smell like a bong man, if it's too clean then it just ain't the same. As nice as it sounds to have a minty bong (by cleaning with mouthwash) taking a hit and getting that menthol flavour ain't too fun.

About boiling your bongs to clean them... I don't like putting glass into boiling water, sure if you put the glass in before you start boiling it shouldn't crack, I still don't like doing it though. It's not really and issue with my random bottle bong, but with nice fancy glass ones that's risky (I don't own any said bongs).