Thanks both! Last time I dealt with this was several years ago; back then a 4000 tank was around $60. Took your advice; bought a replacement tank for $22 Cdn.
How did I know it's only 1/3 used? The front 1/3 of the wadding is lily white, the middle 1/3 is jet black, and the back 1/3 is lily white. Only way I can conceive of filling a tank before the replace counter forces one to replace would be by doing a power clean, and it would be easy enough to add that to the programming logic. Price may be low by 1st world standards, but seems like just another unnecessary insult to the environment to me.