If you've got a pump to run it, I have a large external chamber I use for running carbon when I need it. I'm in Centreville as well, you are welcome to use it. Just need a new mesh sleeve for the carbon, I've run entire 30oz containers of carbon in this filter before Let me know if there is anything I can do to help.
Reason I say if you have a pump, is because the pump I was using died.