Victoria, we have had our Keurig B70 for about two months now. We have never experienced any black residue in our cups or anywhere else after we brew. You didn't say where the residue was...is it in your cup? Now when we use Swiss Miss Chocolate brew it does leave a residue in the bottom but that is easily corrected by just stirring the last of the mixture in your cup....don't know if that helps....David Elliott
Just a thought, are you using flavored coffees in your B70? I haven't seen any issues with the problem like you are describing. We've had our B70 for 8 months now, and the only time I see any type of residue is when we brew a flavored coffee, where the brew leaves behind a "ring" of residual flavoring in the coffee mug.
Have had the same problem especially when using my own grind. The EZ-cup and EZ-cup paper filters takes care of it. The grind needs to be somewhere past standard and less than fine . That is an individual choice. Experimentation with your grinder will give you your answer. I don't have a residue problem with Kcups,just my personal grind. As stated previously,the EZ-cup system will take care of that. Paper filters seem to do the trick. Also, I use the Keurig water filters as recommended and the coffee tastes great! Stir well and enjoy!