[@marko@]

as fishscale said, the DIY CO2 lasts a certain length no matter what tank it is on, what matters is the proportions inside and the amount of initial yeast and the temp and size of the container.
the way it works is by the yeast eating the sugar which is glucose. glucose is C6H12O6. to release the energy inside they break it apart and bond the peices of the molecule with oxygen (O2). the process is:
C6H12O6 + O2 (x6)---> H2O (x6) + CO2 (x6)
the CO2 is a gas and has a lesser density then before so it needs more space. the only place to go is in the tube, into the tank. this process depends on the conditions in the CO2 canister, and are unrelated to those in the tank.