How do you keep the FIZZ in a 2 litre Cola bottle ?????

I once saw a guy use a cola gadget to pump air into it. I guess it was pressurizing the air so the CO2 wouldn't escape. Anyone know if those work ? Where do you buy them ?

I was also thinking you could mix carbonated water but that would dillute it. Maybe one of those funny looking Co2 capsules used for air rifles but how would you use that ?

Dry Ice ? Nah.


Any tinkerers or chemists out there have any ideas ?