I had read a review that stated that this percolator could use all types of pre-ground coffee.  I tried a little of my Maxwell House Dark French roast and it was far too fine to use.  I then went to the grocery store and bought coffee beans and ground them on the largest setting for percolator machines.  Somehow I still ended up with coffee grounds in the bottom of my cup!  I'm going to clean the unit thoroughly and try again.  Hopefully, I'll have better results on my second try:(