Brett, mate...we've got to talk. Next time I come through... I have to be careful here because I'd have to take my socks off to count the number of cups of coffee I've bummed at your place and good coffees they were.
You shouldn't have
any residue in your Mocha machine. I know I'm a Bialetti guy with a flat bottomed aluminium pot and you're a stainless steel round bottomed disciple, but we can put those differences aside and discuss different ways of approaching the best cuppa.
The residue stems from coffee being left to dry out and burn in the bottom of a very hot pot. Here's what I learned in Italy. Leave the lid up during the initial heating period and right through the time it's perking. It won't splash out, believe me. You will both see and hear when the water in the base is getting low. Take it off the burner and pour the brew. Once the pot cools, there should be liquid in the bottom. Rinse it and you should end up with a pretty clean pot.
Here a couple of pics of my little Bialetti to prove my point. It's never been cleaned other than cold water rinse since it was new about four years ago.
Attachment 490640 Attachment 490641
mick :)