Another discussion of KM Quality: http://www.hookahpro.com/forum/showthread.php?t=19381
I am confused, are you sick of shisha and are blaming your equipment as the cause? I know personally I have been trying to keep a good 6+ flavors around and in quantities to keep me entertained and able to mix. I have noticed that some of my personal favorites thus far are very flavorful and that flavor is hard to remove during cleaning. It ends up transferring however minutely over on the next session.
I have found a good freezing (after completely dry) outside for whatever reason really diminishes the robust flavor carry over. Plus using vinegar, lemon juice and some baking soda seems to help as well.