1. Wash it out with warm water (perhaps leaving to stand in water and washing up liquid overnight)

2. If you need to get abrasion use rice or sand (swish the water around inside). Careful with the sand, it can start to scratch the inside of the glass.

3. Get a bottle brush (home brew beer shops are good sources for odd shape brushes) and attack the mineral deposits. They should really just be a sort of dried salt from the previous soda water, so should dissolve using the above techniques quite readily.

4. Some Less severe internal water staining can be removed by pouring enough household bleach to cover the bottom of the bottle into the bottle. The bottle should then be corked or sealed as best you can and left to stand for an hour or two. The theory seems to be the bleach fumes loosen the stain and make it easier to clean with conventional techniques.

And this suggestion from Bob, who clearly has a slightly more evolved view of health and safety than myself: "Rather than domestic bleach to clean I use baby's bottle sterilising tablets. (For vacuum flasks but its the same principle) Not on metal objects though. Leave in overnight." Thanks, clearly a better choice if you're planning to use the syphon - if it's being cleaned just for display purposes, then bleach may not be a big problem, but sterilising tablets are definitely preferable for syphons used for producing drinkable fizz! And like he says, use this for the glass syphons, rather than metal. Thanks Bob!

5. Industrial hand cleaner (Swarfega type) that has small silicon particles in it can be abrasive enough to shift the deposit in conjunction with something to move it around the bottle - one suggestion I read was gravel, but perhaps something like walnuts might be less likely to scratch, although we're starting to get a little exotic here.