CO2 Bell

Will someone please explain how a home made CO2 bell works?
Reading postings in the archives leads me to believe a solid
plastic container is used.  So I can use a small water bottle with
one end cut off.  But how does water continually cycle into the bell
to mix with the CO2 without letting the CO2 escape?  If the bubbles
keep going into the solid bell, it will eventually fill up.  Will diffusion
still continue at that point?

I want to build a DIY yeast CO2 for my 20 gal before investing in a
bigger and better system for a 125 gal tank.  Your help is greatly

Rochelle Williams
williaro at ftmcphsn-emh1_army.mil                  wk:  (404)669-7695
avid gardener and aquarist who does          hm:  (770)389-8360
      a little air pollution work on the side