Not had a soda syphon for about 30 years, but back then you put a couple of tablets in the bottle, and then charged it (made it fizzy) by twisting a small CO2 cannister into the bottle.
I would assume the difference is that a soda machine can do flavours - again, not seen one of them for years either.
Hi Postdog/knobby/heathfield xxx
thanks for all the feedback! Knobby you madman :0/
I've seen a black soda syphon for sale, looks more stylish than a Sodast.... More informed now, thanks! xxx