Search amazon for Soda stream Tank Adapter and you will find things like: https://www.amazon.com/Upgraded-Kit%EF%BC%8C60in-High-Pressure-Stainless-Hose%EF%BC%8C4500PSI/dp/B08HCPHBDC/ref=sr_1_5?keywords=sodastream+tank+adapter&qid=1651080338&sprefix=sodastream+tank+%2Caps%2C131&sr=8-5

You use this to connect a 20lb CO2 tank to your sodastream. You first tank will cost about $100 to $150, but refills are $25 to $50. A single 20lb tank is equivalent to about 23 canisters so it is much cheaper and it comes out at higher pressure (for most of the life of the tank) so you can get more bubbles into your water (and play less in the long run).

I use this hose with a 5lb food grade CO2 tank from Airgas. Its just as simple as hooking one end to the tank, one to the machine, opening the valve, and carbonating your water.

I purchased a 5lb tank from a local beverage dealer that sells them specifically for the Sodastream. Cost me $75 for the initial tank (filled) and then I bring that tank back when it empties and he will refill it for $15.

Then I purchased this hose on Amazon (my Sodastream has the screw-on tank type) and it has worked flawlessly for the family: Upgraded Soda Stream Adapter Hose... https://www.amazon.com/dp/B08HCPHBDC