Refilling SodaStream Canisters

Videos

Very detailed description of the process:

The following has a good list of useful tools, and links to purchase replacement O rings.

Adjustable wrenches to open the canister (One for the valve on the side and one for the main brass fitting.)
Metal bowl to hold the crushed dry ice
Plastic bag to crush the dry ice in
Hammer to crush the dry ice
Funnel to guide the dry ice into the canister
Large spoon to scoop the dry ice out of the bag and into the funnel
Chopstick to push the dry ice through the funnel
Scale to weigh the canister as dry ice is added to it.

Remove the release valve of the canister with a wrench.
Remove the brass fitting at the top of the canister with a wrench.
Put the dry ice pellets in a plastic bag. Using the hammer, crush enough dry ice to fill a canister.
Put the canister on the scale. Press the 'tare' button to weigh just the dry ice added to the canister.
1. Note the net weight of the CO₂ printed on the canister. Typically, this is 935 grams or 33 oz. for a 130 L canister.
2. The net weight is the limit for how much dry ice to add to the canister. Put a little less than this amount to be on the safe side.
Pour the crushed dry ice in the funnel. Make sure the narrow end of the funnel is as wide as possible to prevent clogs. Force the dry ice through using the chopstick.
Replace the brass fitting and release valve.
Set the canister aside until it has iced over on the outside and then returned to the ambient temperature.