Review on Efficient Co2 Adapter: Connect SodaStream to Paintball Co2 Refill - 60 inch Hose with Accessory Kit - Direct Connect to TR21-4 - Co2 Adapter for 20 lb Tanks by Jesus Baker

I recommend this upgrade for cost savings and convenience. After the initial outlay of $25 to fill a 5 pound CO2 tank, you're looking at a marginal cost of 8-15 *cents* per gallon of sparkling water. Not to mention that you no longer have to lug things from the supermarket. For additional savings, you can flavor confectionery essential oils and buy (or 3D print) a sparkling water adapter in standard 1 liter PET bottles. both the CO2 tank and the sodastream inlet. The narrow plastic neck leading to the Sodastream's CO2 inlet made it very difficult to tighten with a wrench, but pliers did the trick. The included rubber grommet for the quick connector didn't allow the hose to be inserted far enough for the latch to engage, but the lack of a grommet meant no leaks so no damage was done.