Digital BW, The Print

Switching from one inkset to another often leaves a lot of 
"unusable" ink behind. For example, I´ve been running out of  the 
piezo yellow-substitute on my 1160, while my black and cyan 
stays more than half full and magenta has a reasonable rest too. 
I´m running another 1160 with MIS FS, which is as good as piezo 
but much cheaper and a third set aof MIS VM on a 1290 (I have 
been a bit euphoric in testing, once). I do not want to buy piezo 
inks again  so must I pour out  the piezo-rest into the sink or can 
I use it with any of the other inksets ?

Paul, could you perhaps elabaorate on this problem a bit.
Which inks of the different sets can substitute each other:
PiezoBW, MIS FS, MIS VM ?
Martin, perhaps we can put a summary to the files section?
Thanks Bernd