I found information on the Internet that one can order an adapter that allows me to fill CO2 bottles, obtainable from an e-mail address:Mcleverpeople@aol.com
So I sent the following mail:

Hello, I found your e-mail address at soadahclub and I want to fill my SodastreamCO2 bottle from a larger 6kg pub bottle. On soadahclub I am told I can purchase the Adaptor from you. Can I do that?
How much does it cost?
Can I pay with Paypal or credit card?
I received an answer which finished with:

You can order here! My PayPal account >mcleverpeople@aol.com < (PayPalAccount + 1,90 Euros more)

Price Spar-Adapter 38 Euros postage insured by airmail 10,50 Euros completely 48,50 Euros PayPal   + 1,90 Euro total 50,40 Euros

At Paypal you can pay from your PayPal account or with your credit card. I have a PayPal account which is much more secure than a credit card. It does not costanything so many vendors on the Internet have Paypal as a method of payment.

I paid with PayPal and about 2 weeks later the adapter was delivered by post from Germany.

This is how I fill a CO2 bottle for fizzy drinks from a large pub bottle

This is a method that suits me, it does not follow the supplied instructions.

So, anyway, this is the way I do it. First I put the empty CO2 bottle in the freezer for a few hours so it becomes about minus 15 – 20 degrees Celsius cold. This is because a cold bottle accepts more CO2, filling takes place at bottle pressure and not with a pump. By cooling the receiving bottle the pressure in it is reduced.

I have screwed on the adapter to my 6kg pub bottle that costs €25 to fill with food quality CO2 (have bargained, easy to do when you are helping the environment).

CO2 bottles for drinks have a tube internally that reaches the bottom. (CO2 extinguishers do not have a tube) so what comes out is liquid CO2, so I do not have to upturn the bottle. The adapter can only fit one way, with different threads for the big and little bottle.

I fit the little adapter by hand. Then I open fully quickly and wait for it to stop blowing, about one minute. Close the valve, unscrew the little bottle and weigh it. Empty weight is marked on the bottle 790 grammes, with 425 grammes of CO2. The bottle when full weighs 1215 grammes.

I get about 100 grammes with one filling so I return the bottle to the freezer.

When frozen I repeat the filling. I do that four times and arrive just under 1200 grammes full weight. That is enough; I have filled just about 400 grammes.

Have filled a fifth time but the bottle is overfull so I release some CO2.

This method suits me fine. When I am at the freezer and a recharge is needed I do it.

A one minute job done four times is much easier than driving off to buy expensive CO2.

425 grammes CO2 cost EURO 9 in the shop, that is EURO 21/kg. My large bottle costs EURO 25 to fill, EURO 1.8 to fill the 425 gram fizzy drink bottle. This cost I recover just by not having to drive to the shop so that after 6 fillings the adapter is paid for.

Sodastream CO2 cylinder filled slower instead

I use AGA:s (Wassermaxx) CO2 bottles to both my Wassermaxx and my Soda- stream. This is because the CO2 in the bottle that was supplied with the Sodastream tasted horrible, so I changed it for an AGA CO2 bottle when I bought my Sodastream Design machine.

So I have experimented with another Sodastream CO2 bottle just to see if it works.

First I could not get the bottle to fill. Full stop. Looked on the Internet, Sodastream have a patent that gets the valve to close when the pressure is too high. To stop others from filling their CO2 bottles…

So I tried just opening the valve a little on the pub bottle. Doing this the Sodastream bottle filled without any problem.

Old 300 grammes Sodastream bottles?

If anyone wonders, the adaptor does not fit the old 300 gramme Sodastream steel bottles. These have another screw thread. Today CO2 bottles must have a certain screw thread, different for different gases to prevent accidents. It must not be at all possible to attach the wrong gas in industry and medicine.