What are the ingredients in the box? I use LemiShine to clean my dishwasher. LemiShine is citric acid. It works GREAT! The first time (after many years of not cleaning it) I had to run it twice. I had actual rocks of calcium blocking the rotating arms. The LemiShine cleaned all that out. I use it both with and without dishes with no problems...although there is some question as to whether the Lemishine removed the red lettering from the Pyrex measuring cups.

LemiShine is the dishwasher detergent I use (for the dishes). Works great.

Because if there is "stuff" in your dishwasher the cleaner won't get at all parts of the dishwasher as well as if it were empty. and the cleaner may not be very kind to certain metal things.

I've tried Lemishine. I tried vinegar. The Cascade cleaner worked the best.

The reason that you clean it when it's empty is so that the water and cleaner can hit all parts of the dishwasher unobstructed by dishes or lasagna pans. Pans especially can block some of the water.