Digital BW, The Print

I have a relatively new Epson 1280 employing an MIS UT2 inkset.  I am 
using spongeless cartridges and refilling the ink manually -- a great, 
money-saving convenience.  However, my print heads seem to be clogging, 
requiring repeated cleaning cycles, if the printer sits idle for even a 
day.  Has anyone else experienced this?  Or -- is it possible that I'm 
introducing air bubbles during the refill process and experiencing 
"vapor lock"?   If so, how should I correct my refilling technique?

Many thanks,

Craig Roberts
Washington, DC