Well if its filled its pretty easy, hold it horizontal and keep rotating it around (as if u were rolling it along) not top over bottom. If the Co2 changes from white to clear at one stage u can bet thats where the anti-siphon is. Other than that i dont know how u can tell.
As was said...whe you get a big cloud of liquid come out..thats when the anti sypnon is at the bottom, ie, lowermost with the bottle horizontal....make sure that you markw th etop of the bottle, so that when it screws in to the ASA, you can turn it so th eanti syphon is at the top.
Are you sure? I thought the anti-syphon was a bent, rigid tube (quiet at the back!) whereas a syphon tube is a weighted flexible one, which would make a noise as it clunks about the inside.
I'll have to try out the rotating trick, though. My co2 tank had it marked with a sharpie pen that's now rubbed off. bogger.
Must be loose then..if you think about it...it stands to reason that the long flexible pipe used for syphons, reach to the bottom of the bottle to draw liquid with...anti syphons curve up the neck of the bottle to th eeupermost part, in order to draw gas...and they are solid, short pipes so shouldnt move/ring.....